Add reference to Cloud docs

docs/docs/cloudimages.md

@@ -22,6 +22,7 @@ these images can be selected for installation from <a href="https://openstack.ce
 </ul>
 where YYYY-MM-DD correspond to year-month-day of release.
 <p>
+More information can be found in the <a href="https://clouddocs.web.cern.ch/details/standard_images.html">Cloud user guide</a>. availability of older images can be found here as well.
 
 <hr>
 <h2>Images content</h2>