dashboard: add help text to vm-list

circle/dashboard/templates/dashboard/vm-list.html

@@ -102,6 +102,9 @@
 </div>
 </div>
 
+<div class="alert alert-info">
+  You can filter the list by certain attributes (owner, name, status, tags) in the following way: "owner:John Doe name:my little server". If you don't specify any attribute names the filtering will be done by name.
+</div>
 
 <div class="alert alert-info">
   {% trans "You can select multiple vm instances while holding down the <strong>CTRL</strong> key." %}