add github link

index.html

@@ -17,6 +17,7 @@
     <p>No IE support so far, only tested with recent Chrome, Opera,
     and Firefox builds. The JavaScript parser is the only one I've
     ported over.</p>
+    <p>Code at <a href="https://github.com/marijnh/codemirror2">https://github.com/marijnh/codemirror2</a>.</p>
     <div id="code" style="font-family: monospace"></div>
     <textarea id="input" style="display: none">
 // Demo code (the actual new parser character stream implementation)