fix path to extensions page

doc/_templates/index.html

@@ -33,7 +33,7 @@
       href="http://pygments.org">Pygments</a> highlighter</li>
     <li><b>Extensions:</b> automatic testing of code snippets, inclusion of
       docstrings from Python modules (API docs), and
-      <a href="{{ pathto('ext') }}">more</a></li>
+      <a href="{{ pathto('extensions') }}">more</a></li>
   </ul>
   <p>
     Sphinx uses <a href="http://docutils.sf.net/rst.html">reStructuredText</a>