doc: convert README to markdown

Author: remdub

README.md

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+[![Latest Version](https://img.shields.io/pypi/v/collective.big.bang.svg)](https://pypi.python.org/pypi/collective.big.bang/)
+[![Tests Status](https://github.com/collective/collective.big.bang/actions/workflows/test.yml/badge.svg)](https://github.com/collective/collective.big.bang/actions/workflows/test.yml)
+![Supported - Python Versions](https://img.shields.io/pypi/pyversions/collective.big.bang.svg?style=plastic)
+[![License](https://img.shields.io/pypi/l/collective.big.bang.svg)](https://pypi.python.org/pypi/collective.big.bang/)
+
+# collective.big.bang
+
+```
+Our whole universe was in a hot, dense state
+Then nearly fourteen billion years ago expansion started, wait
+The earth began to cool, the autotrophs began to drool
+Neanderthals developed tools
+We built a wall (we built the pyramids)
+Math, science, history, unraveling the mysteries
+That all started with the big bang! Hey!
+```
+
+So all started with the Plone site! Hey!
+This package is used to create a Plone site when Zope is started (just before the `Ready to handle requests` sentence).
+
+You can use environment variables to create the Plone site and choose which packages you would like to install. See "Environment variables".
+
+### Why not use `collective.recipe.plonesite`?
+
+The goal is to create the Plone site when you deploy a new Plone in a containerized environment.
+We think it's easier to create the Plone site on start-up, without an entrypoint or extra commands.
+It's simpler in a containerized environment than starting a buildout part to create a Plone site.
+
+---
+
+**Fun fact:**
+This package is now called `collective.big.bang` instead of the original `collective.bigbang`, because the name `collective.bigbang` was rejected by PyPI.
+
+## Environment variables
+
+You can add environment variables into your buildout under the `instance` part using `environment-vars`:
+
+```
+...
+[instance]
+...
+environment-vars =
+    PLONE_EXTENSION_IDS plone.app.caching:default,plonetheme.barceloneta:default
+    DEFAULT_LANGUAGE fr
+    ADMIN_PASSWORD mysuperpa$$w0rd
+    ACTIVE_BIGBANG True
+```
+
+Or use tools like [`direnv`](https://direnv.net/) (example `.envrc` file):
+
+```bash
+export PLONE_EXTENSION_IDS=plone.app.caching:default,plonetheme.barceloneta:default
+export DEFAULT_LANGUAGE=fr
+export ADMIN_PASSWORD=mysuperpa$$w0rd
+export ACTIVE_BIGBANG=True
+```
+
+### `PLONE_EXTENSION_IDS`
+A list of GenericSetup profiles to install.
+**Default:** `plone.app.caching:default,plonetheme.barceloneta:default`
+
+### `DEFAULT_LANGUAGE`
+The default language of the Plone site.
+**Default:** `en`
+
+### `ADMIN_PASSWORD`
+The password for the Zope "admin" user.
+**Note:** No default. If not set, the admin password will not be updated.
+
+### `ACTIVE_BIGBANG`
+Create a Plone site on this instance.
+Used to avoid conflict errors; should be `True` on only one instance.
+**Default:** `False`
+
+---
+
+## Features
+
+- Creates Plone site when Zope is started.
+
+## Installation
+
+Install `collective.big.bang` by adding it to your `buildout`:
+
+```
+[buildout]
+
+...
+
+eggs +=
+    collective.big.bang
+
+...
+
+[instance]
+...
+environment-vars =
+    PLONE_EXTENSION_IDS plone.app.caching:default,plonetheme.barceloneta:default
+    DEFAULT_LANGUAGE fr
+    ADMIN_PASSWORD mysuperpa$$w0rd
+    ACTIVE_BIGBANG True
+```
+
+Then run:
+
+```bash
+bin/buildout
+```
+
+## Contribute
+
+- [Issue Tracker](https://github.com/collective/collective.big.bang/issues)
+- [Source Code](https://github.com/collective/collective.big.bang)
+
+## Support
+
+If you're having issues, please let us know by opening an issue.
+
+## License
+
+The project is licensed under the **GPLv2**.