docs: add GH button in support of Ukraine (#1134)

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.

Pull Request resolved: https://github.com/facebook/yoga/pull/1134

Reviewed By: cortinico

Differential Revision: D34635677

Pulled By: dmitryvinn-fb

fbshipit-source-id: 492fb66b9d4cb218f422564dcef24089c2847603

README.md

@@ -1,4 +1,4 @@
-# Yoga [![CocoaPods](https://img.shields.io/cocoapods/v/YogaKit.svg)](http://cocoapods.org/pods/YogaKit) [![npm](https://img.shields.io/npm/v/yoga-layout.svg)](https://www.npmjs.com/package/yoga-layout) [![bintray](https://img.shields.io/bintray/v/facebook/maven/com.facebook.yoga:yoga.svg)](https://bintray.com/facebook/maven/com.facebook.yoga%3Ayoga/_latestVersion) [![NuGet](https://img.shields.io/nuget/v/Facebook.Yoga.svg)](https://www.nuget.org/packages/Facebook.Yoga)
+# Yoga [![Support Ukraine](https://img.shields.io/badge/Support-Ukraine-FFD500?style=flat&labelColor=005BBB)](https://opensource.fb.com/support-ukraine) [![CocoaPods](https://img.shields.io/cocoapods/v/YogaKit.svg)](http://cocoapods.org/pods/YogaKit) [![npm](https://img.shields.io/npm/v/yoga-layout.svg)](https://www.npmjs.com/package/yoga-layout) [![bintray](https://img.shields.io/bintray/v/facebook/maven/com.facebook.yoga:yoga.svg)](https://bintray.com/facebook/maven/com.facebook.yoga%3Ayoga/_latestVersion) [![NuGet](https://img.shields.io/nuget/v/Facebook.Yoga.svg)](https://www.nuget.org/packages/Facebook.Yoga)
 
 ## Building
 Yoga builds with [buck](https://buckbuild.com). Make sure you install buck before contributing to Yoga. Yoga's main implementation is in C++, with bindings to supported languages and frameworks. When making changes to Yoga please ensure the changes are also propagated to these bindings when applicable.