[Documentation] Replace dead link to Flax install guide (#3739)

Replace dead link to Flax documentation

Replace the dead link to the Flax installation guide by a working one: https://flax.readthedocs.io/en/latest/#installation

README.md

@@ -25,7 +25,7 @@
 
 ## Installation
 
-We recommend installing 🤗 Diffusers in a virtual environment from PyPi or Conda. For more details about installing [PyTorch](https://pytorch.org/get-started/locally/) and [Flax](https://flax.readthedocs.io/en/latest/installation.html), please refer to their official documentation.
+We recommend installing 🤗 Diffusers in a virtual environment from PyPi or Conda. For more details about installing [PyTorch](https://pytorch.org/get-started/locally/) and [Flax](https://flax.readthedocs.io/en/latest/#installation), please refer to their official documentation.
 
 ### PyTorch