docs: add GH button in support of Ukraine (#147)

Summary:
Our mission at [Meta Open Source](https://opensource.fb.com/) 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.

Pull Request resolved: #147

Reviewed By: simonmar

Differential Revision: D34649194

Pulled By: dmitryvinn-fb

fbshipit-source-id: 6bb709a7ed5587667f13aadd7facba04ca9d3546

Author: dmitryvinn

readme.md

@@ -2,7 +2,7 @@
 
 # Haxl
 
-[![Build Status](https://travis-ci.org/facebook/Haxl.svg?branch=master)](https://travis-ci.org/facebook/Haxl)
+[![Support Ukraine](https://img.shields.io/badge/Support-Ukraine-FFD500?style=flat&labelColor=005BBB)](https://opensource.fb.com/support-ukraine) [![Build Status](https://travis-ci.org/facebook/Haxl.svg?branch=master)](https://travis-ci.org/facebook/Haxl)
 
 Haxl is a Haskell library that simplifies access to remote data, such
 as databases or web-based services. Haxl can automatically