- add sortable listing image

Resources/doc/cookbook/recipe_sortable_listing.rst

@@ -9,7 +9,10 @@ Background
 A sortable behavior is already available for one-to-many relationships (http://sonata-project.org/bundles/doctrine-orm-admin/master/doc/reference/form_field_definition.html#advanced-usage-one-to-many). 
 However there is no packaged solution to have some up and down arrows to sort your records such as showed in the following screen
 
-list.jpg
+.. figure:: ../images/admin_sortable_listing.png
+   :align: center
+   :alt: Sortable listing
+   :width: 700px
 
 
 Pre-requisites