Added fork me on github ribbon

Author: shinglyu

index.html

@@ -25,5 +25,7 @@ <h1>RustPython Demo</h1>
     <button id="run-btn">Run</button>
     <h2>Open the browser console (<kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>I</kbd> or <kbd>F12</kbd>) to see the output</h2>
     <script src="./bootstrap.js"></script>
+
+    <a href="https://github.com/RustPython/RustPython"><img style="position: absolute; top: 0; right: 0; border: 0;" src="https://s3.amazonaws.com/github/ribbons/forkme_right_green_007200.png" alt="Fork me on GitHub"></a>
   </body>
 </html>