Updated link to upgrade page in wiki.

git-svn-id: http://svn.igniterealtime.org/svn/repos/wildfire/trunk@7225 b35dd754-fafc-0310-a699-88a17e54d16e

documentation/docs/index.html

@@ -31,7 +31,7 @@ messaging (IM) services using the XMPP protocol.
         How to install Wildfire.
     </li>
     <li>
-        <a href="install-guide.html">Upgrade Guide</a> -
+        <a href="http://wiki.igniterealtime.org/display/WILDFIRE/Wildfire+Upgrade+Guide">Upgrade Guide</a> -
         Instructions for upgrading an existing Wildfire installation.
     </li>
     <li>