Add GitHub icon

Author: Sunderlandkyl

_includes/themes/twitter/top.html

@@ -43,7 +43,10 @@ <h2>Contact</h2>
 
 <div class="row">
   <div class="span4">
-    <h2>GitHub</h2>
+    <h2>
+      <img style="height: 1em; vertical-align:top" src="images/GitHub-Mark-32px.png"></img>
+      GitHub
+    </h2>
     <p>See the source code on GitHub.</p>
     <p><a class="btn" href="https://github.com/PlusToolkit/PlusLib">View source code &raquo;</a></p>
   </div>