docs(jqLite): document that append doesn't work well with a multi-node object

Contrary to jQuery jqLite's append doesn't clone elements so will not work
correctly when invoked on a jqLite object containing more than one DOM node.

Refs angular#11446
Closes angular#16517

Author: mgol

src/jqLite.js

@@ -54,7 +54,8 @@
  *
  * - [`addClass()`](http://api.jquery.com/addClass/) - Does not support a function as first argument
  * - [`after()`](http://api.jquery.com/after/)
- * - [`append()`](http://api.jquery.com/append/)
+ * - [`append()`](http://api.jquery.com/append/) - Contrary to jQuery, this doesn't clone elements
+ *   so will not work correctly when invoked on a jqLite object containing more than one DOM node
  * - [`attr()`](http://api.jquery.com/attr/) - Does not support functions as parameters
  * - [`bind()`](http://api.jquery.com/bind/) (_deprecated_, use [`on()`](http://api.jquery.com/on/)) - Does not support namespaces, selectors or eventData
  * - [`children()`](http://api.jquery.com/children/) - Does not support selectors