updating docs

Author: lauren mccarthy

docs/yuidoc-p5-theme/layouts/main.handlebars

@@ -68,6 +68,7 @@
       <li><a href="../libraries/">Libraries</a></li>
       <li><a href="../learn/">Learn</a></li>
       <li><a href="../contribute/">Contribute</a></li>
+      <li><a href="http://forum.processing.org/two/" target=_blank class="other-link">Forum</a></li>
       <li><a href="http://github.com/lmccart/p5.js" target=_blank class="other-link">Github</a></li>
       <li><a href="http://twitter.com/p5xjs" target=_blank class="other-link">Twitter</a></li>
     </ul>