docs(CONTRIBUTING): add jquery-ui-sortable example

Author: thgreasi

CONTRIBUTING.md

@@ -7,3 +7,6 @@ Feel free to edit any of them for your needs (don't forget to also update the li
 
 * [Simple Demo](http://codepen.io/thgreasi/pen/jlkhr)
 * [Connected Lists](http://codepen.io/thgreasi/pen/uFile)
+
+Since some issues may be caused by jquery-ui-sortable and not by the wrapping that angular-ui-sortable does,
+please try your use case using [this plain jquery-ui sortable example](http://codepen.io/thgreasi/pen/rarQvR) before opening a new issue in the repositry.