Added sponsor button

Author: pshihn

Diff for: index.html

@@ -266,6 +266,11 @@ <h3>No Animation</h3>
             <button>View on Github</button>
           </a>
         </p>
+        <p>
+          <a target="_blank" href="https://opencollective.com/rough" rel="noopener">
+            <button>Sponsor this project</button>
+          </a>
+        </p>
         <p>
           Reach out on twitter <a style="color: #0d47a1; font-weight: bold;" href="https://twitter.com/preetster"
             target="_blank" rel="noopener">@preetster</a>