[JAX/Imagen] Imagen model with reference to Rosetta Github

JAX/MultiModal/Imagen/README.md

@@ -0,0 +1,2 @@
+# Imagen on GPUs
+Please refer to [Rosetta Imagen](https://github.com/NVIDIA/JAX-Toolbox/tree/main/rosetta/rosetta/projects/imagen), NVIDIA's project that enables seamless training of LLMs, CV models and multimodal models in JAX, for information about running Imagen models and experiments on GPUs.