doc improvement

core/src/main/resources/lib/form/repeatableProperty.jelly

@@ -26,7 +26,16 @@ THE SOFTWARE.
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:d="jelly:define" xmlns:l="/lib/layout" xmlns:t="/lib/hudson" xmlns:f="/lib/form">
   <st:documentation> <![CDATA[]
     Data-bound only version of <f:repeatable> that assumes the type pointed by the property is data-bound as well.
-  ]]>
+    The nested property type must be Describable and it needs to have config.jelly.
+
+    The nested configuration fragment normally needs to have a delete button by adding a fragment like this:
+
+      	<f:entry title="">
+          <div align="right">
+            <f:repeatableDeleteButton />
+          </div>
+        </f:entry>
+    ]]>
 
     <st:attribute name="field">
       Used for the data binding.