dashboard: add placeholder to group textbox

circle/dashboard/templates/dashboard/group-detail.html

@@ -48,7 +48,7 @@
         </tr>
   </tbody>
   </table>
-    	  <textarea name="list-new-namelist" class="form-control"></textarea>
+    	  <textarea name="list-new-namelist" class="form-control" placeholder="{% trans "To add more users, list the name of users in multiple lines" %}"></textarea>
   <div class="form-actions">
     <button type="submit" class="btn btn-success">{% trans "Save" %}</button>
   </div>