[RFCs] Add rfcs directory

rfcs/README.md

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+# oneTBB Design Documents/RFCs
+
+The RFC process intends to:
+
+- Communicate library-wide changes
+- Collect feedback before implementation
+- Increase transparency in decision-making 
+- Align different teams involved in oneTBB development
+
+This directory contains design documents (RFCs) approved 
+or rejected for implementation in oneTBB.
+
+The possible RFC states are:
+
+1. Initial 
+2. Proposed
+3. Experimental
+4. Supported
+5. Archived
+
+Most modifications or new features will naturally start as a part of a 
+GitHub issue or discussion. Small changes do not require a formal RFC. 
+However, if the issue or discussion results in an idea for a significant 
+change or new feature that affects the library's public API or architecture, 
+we recommend opening a PR to add a new RFC to the `rfcs/proposed` directory. 
+The RFC should provide a detailed description and design of the proposed feature.
+or new feature that significantly impacts the library's public API or 
+architecture, it will be suggested that a PR be opened to add a new rfc 
+to the `rfcs/proposed` directory. The RFC contains a more detailed description
+and design for the feature.
+
+## General Process
+
+A template for RFCs is available as [template.md](template.md). Place the modified
+template in the subdirectory of the `rfcs/proposed` with a name
+of the form `<feature>_<extension_description>`. For example,
+a proposal for a new ``my_op`` flow graph node should be put into the
+`rfcs/proposed/flow_graph_my_op_node` directory. Use [template.md](template.md) 
+to create the `README.md` file in that directory. The folder can 
+contain other files referenced by the `README.md` file, such as figures.
+
+Once two maintainers approve the PR, it is merged into the `rfcs/proposed`
+directory. Update the RFC document with additional information as the RFC moves 
+to different states. 
+
+A proposal that is subsequently implemented and released in oneTBB 
+as a preview feature is moved into the `rfcs/experimental` folder. The
+RFC for a preview feature in `rfcs/experimental` should include a description
+of what is required to move from experimental to fully supported -- for 
+example, feedback from users, demonstrated performance improvements, etc.
+
+A proposal that is implemented, added to the oneTBB specification, and 
+supported as a full feature appears in the `rfcs/supported` directory. An RFC 
+for a fully supported feature in the `rfcs/supported` directory should 
+have a link to the section in the oneTBB specification with its 
+formal wording.
+
+A feature that is removed or a proposal that is abandoned or rejected will 
+be moved to the `rfcs/archived` folder.
+
+## Document Style
+
+The design documents are stored in the `rfcs` directory, and each RFC is placed 
+in its subdirectory under `rfcs/proposed/<feature>_<extension_description>`. 
+
+- There must be a `README.md` file that contains the main RFC itself (or 
+links to a file that contains it in the same directory).
+  - The RFC should follow the [template.md](template.md) structure. 
+  - The directory can contain other supporting files, such as images, tex 
+  formulas, and sub-proposals / sub-RFCs.
+  - We highly recommend using a text-based file format like markdown for easy 
+  collaboration on GitHub, but other formats like PDFs may also be acceptable.
+- For the markdown-written RFC, keep the text width within
+  100 characters, unless there is a reason to violate this rule, e.g., 
+  long links or wide tables.
+- It is also recommended to read through existing RFCs to better understand the 
+general writing style and required elements.

rfcs/archived/README.md

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+# Archived Design Documents
+
+Documents may appear in the `rfcs/archived` directory for one of 
+two reasons:
+
+1. The document describes a feature or extension that has been deprecated and 
+then removed.
+2. The document describes a proposed feature or extension that have
+not (ultimately) become a fully supported feature. 
+
+Design documents that appear in the `rfcs/archived` folder should describe a 
+reason for archiving.  Documents may 
+remain in this folder indefinitely to serve as a source of information about
+previous proposals and features.

rfcs/experimental/README.md

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+# Design Documents for Experimental Features
+
+Experimental proposals describe extensions that are implemented and
+released as preview features in the oneTBB library. A preview
+feature is expected to have an implementation that is of comparable quality
+to a fully supported feature. Sufficient tests are required.
+
+An experimental feature does not yet appear as part of the oneTBB 
+specification. Therefore, the interface and design can change.
+There is no commitment to backward compatibility for a preview
+feature.
+
+The documents in this directory 
+should include a list of the exit conditions that need to be met to move from
+preview to fully supported. These conditions might include demonstrated
+performance improvements, demonstrated interest from the community,
+acceptance of the required oneTBB specification changes, etc. 
+
+For features that require oneTBB specification changes, the document might
+include wording for those changes or a link to any PRs that opened
+against the specification.
+
+Proposals should not remain in the experimental directory forever.
+It should move either to the
+supported folder when they become fully supported or the archived 
+folder if they are not fully accepted. It should be highly unusual for 
+a proposal to stay in the experimental folder for longer than a year or 
+two.

rfcs/proposed/README.md

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+# Design Documents for Proposed Features
+
+Proposed features in this directory have reached some level of consensus within the 
+community, indicating that they have potential and deserve further development. 
+However, the proposed changes have not yet been released as a
+preview or fully supported feature of the library.
+
+RFCs in the `rfcs/proposed` directory should explain the motivation,
+design, and open questions related to the proposed extension.

rfcs/supported/README.md

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+# Design Documents for Supported Features
+
+Supported proposals describe extensions implemented and
+released as fully supported features of the oneTBB library. A fully supported
+feature has a high-quality implementation. If the proposal impacted the
+public API of the library, it should appear in the oneTBB specification and
+have supporting documentation in the oneTBB Reference as needed. A fully 
+supported feature is regularly tested.
+
+Proposals that appear in `rfcs/supported` may be retained indefinitely to
+provide insight into the design of existing features.

rfcs/template.md

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+# Descriptive Name for the Proposal
+
+## Introduction
+
+Short description of the idea proposed with explained motivation. 
+
+The motivation could be:
+- Improved users experience for API changes and extensions. Code snippets to
+  showcase the benefits would be nice here.
+- Performance improvements with the data, if available.
+- Improved engineering practices.
+
+Introduction may also include any additional information that sheds light on
+the proposal, such as history of the matter, links to relevant issues and
+discussions, etc.
+
+## Proposal
+
+A full and detailed description of the proposal with highlighted consequences.
+
+Depending on the kind of the proposal, the description should cover:
+
+- New use cases supported by the extension.
+- The expected performance benefit for a modification. 
+- The interface of extensions including class definitions or function 
+declarations.
+
+A proposal should clearly outline the alternatives that were considered, 
+along with their pros and cons. Each alternative should be clearly separated 
+to make discussions easier to follow.
+
+Pay close attention to the following aspects of the library:
+- API and ABI backward compatibility. The library follows semantic versioning
+  so if any of those interfaces are to be broken, the RFC needs to state that
+  explicitly.
+- Performance implications, as performance is one of the main goals of the library.
+- Changes to the build system. While the library's primary building system is
+  CMake, there are some frameworks that may build the library directly from the sources.
+- Dependencies and support matrix: does the proposal bring any new
+  dependencies or affect the supported configurations?
+
+Some other common subsections here are:
+- Discussion: some people like to list all the options first (as separate
+  subsections), and then have a dedicated section with the discussion.
+- List of the proposed API and examples of its usage.
+- Testing aspects.
+- Short explanation and links to the related sub-proposals, if any. Such
+  sub-proposals could be organized as separate standalone RFCs, but this is
+  not mandatory. If the change is insignificant or doesn't make any sense
+  without the original proposal, you can have it in the RFC.
+- Execution plan (next steps), if approved.
+
+## Open Questions
+
+For new proposals (i.e., those in the `rfcs/proposed` directory), list any
+open questions.