list available modes on index page

index.html

@@ -68,6 +68,16 @@ StringStream.prototype = {
       });
     </script>
 
+    <h3>Available modes:</h3>
+
+    <ul>
+      <li><a href="mode/javascript/">JavaScript</a></li>
+      <li><a href="mode/xml/">XML/HTML</a></li>
+      <li><a href="mode/css/">CSS</a></li>
+      <li><a href="mode/htmlmixed/">Mixed-mode HTML</a></li>
+      <li><a href="mode/diff/">Diff</a></li>
+    </ul>
+
     <h3>CodeMirror 2 has entered beta!</h3>
 
     <p>Beta 1 was released on February 8th 2011. There are no release