docs: add GH button in support of Ukraine (#949)

* Adding ELI5 video to Fairscale

* docs: add GH button in support of Ukraine

## Summary:
Our mission at Meta Open Source is to empower communities through open source, and we believe that it means building a welcoming and safe environment for all. As a part of this work, we are adding this banner in support for Ukraine during this crisis.

README.md

 ![FairScale Logo](./docs/source/_static/img/fairscale-logo.png)
 
+[![Support Ukraine](https://img.shields.io/badge/Support-Ukraine-FFD500?style=flat&labelColor=005BBB)](https://opensource.facebook.com/support-ukraine)
 ![PyPI](https://img.shields.io/pypi/v/fairscale)
 [![Documentation Status](https://readthedocs.org/projects/fairscale/badge/?version=latest)](https://fairscale.readthedocs.io/en/latest/?badge=latest)
 [![CircleCI](https://circleci.com/gh/facebookresearch/fairscale.svg?style=shield)](https://app.circleci.com/pipelines/github/facebookresearch/fairscale/) ![PyPI - License](https://img.shields.io/pypi/l/fairscale) [![Downloads](https://pepy.tech/badge/fairscale)](https://pepy.tech/project/fairscale) [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](https://github.com/facebookresearch/fairscale/blob/main/CONTRIBUTING.md)