Update index.html

Author: stampylongr

index.html

@@ -8,6 +8,7 @@
       <li><a href="powerlineio.html">POWERLINE.io</a></li>
       <li><a href="smf.html">Super Mario Flash</a></li>
       <li><a href="nblox.html">n-blox</a></li>
+      <li><a href="xkcd.html">xkcd CLI</a></li>
     </ul>
     <p>there will be more games added soon!</p>
     <br />