doc(readme): ddpm paper

Author: pierrot-lc

README.md

@@ -1,7 +1,8 @@
 # Simple DDPM
 
-This repository is a `jax` implementation of the *Denoising Diffusion
-Probabilistic Models*. The model is trained on the [`anime
+This repository is a `jax` implementation of the  *Denoising Diffusion
+Probabilistic Models* [paper](https://arxiv.org/abs/2006.11239). The model is
+trained on the [`anime
 face`](https://www.kaggle.com/datasets/splcher/animefacedataset) kaggle
 dataset.
 
@@ -75,5 +76,6 @@ This is what motivated me to build a minimal implementation and helped me a lot
 understanding the equations.
 
 - [Anime Face Dataset](https://www.kaggle.com/datasets/splcher/animefacedataset)
+- [Denoising Diffusion Probabilistic Models](https://arxiv.org/abs/2006.11239)
 - [Tutorial on Diffusion Models for Imaging and Vision](https://arxiv.org/abs/2403.18103)
 - [U-ViT paper](https://arxiv.org/abs/2209.12152)