added cron constructs like @weekly (#1255)

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@7013 71c3de6d-444a-0410-be80-ed276b4c234a

war/resources/help/project-config/timer-format.html

@@ -37,6 +37,9 @@
   </ul>
   <p>
     Empty lines and lines that start with '#' will be ignored as comments.
+  </p><p>
+    In addition, '@yearly', '@annually', '@monthly', '@weekly', '@daily', '@midnight',
+    and '@hourly' are supported.
   </p>
   <table>
     <tr>