Adding Social Banner in Support of Ukraine (#1556)

Summary:
Our mission at [Meta Open Source](https://opensource.facebook.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.

## Testing
<img width="1080" alt="image" src="https://user-images.githubusercontent.com/12485205/156466214-8b43b13c-617a-4167-a982-d5658173d33e.png">

Pull Request resolved: #1556

Reviewed By: candance

Differential Revision: D34647758

Pulled By: dmitryvinn-fb

fbshipit-source-id: c66c38a0f195abc5285cab449cb825ac16bb8496

docs/css/jazzy.css

@@ -127,6 +127,20 @@ header {
     height: 10px;
     margin: 0 5px; }
 
+/* Social Banner */
+.socialBanner {
+  font-weight: bold;
+  font-size: 20px;
+  padding: 20px;
+  max-width: 768px;
+  margin: 0 auto;
+  color: black;
+  text-align: center;
+}
+.socialBanner a {
+  text-decoration: underline;
+}
+
 .sidebar {
   background-color: #f9f9f9;
   border: 1px solid #e2e2e2;

docs/index.html

@@ -309,6 +309,9 @@
     </a>
 </p>
 
+<div class="socialBanner">
+  Support Ukraine 🇺🇦  <a href="https://opensource.facebook.com/support-ukraine">Help Provide Humanitarian Aid to Ukraine</a>.
+</div>
 <hr>
 
 <p>A data-driven <code>UICollectionView</code> framework for building fast and flexible lists.</p>