Add link to latest documentation in 404 page

Author: jamesfredley

pages/404.html

@@ -16,6 +16,7 @@ <h2>What can you do?</h2>
         <ul>
             <li>Check the URL for typing errors</li>
             <li>Return to the <a href="/">home page</a></li>
+            <li>Read the <a href="/docs/latest/">latest documentation</a></li>
             <li>Visit our <a href="/learning.html">learning resources</a></li>
             <li>Explore the <a href="/community.html">Grails community</a></li>
         </ul>