Update form_collections.rst

Added link to Doctrine docs - same as 8bca82a

Author: ThomasLandauer

form/form_collections.rst

@@ -47,7 +47,7 @@ Here's the ``Task`` and the ``Tag`` entity::
 
 .. note::
 
-    The ``ArrayCollection`` is specific to Doctrine and is basically the
+    The `ArrayCollection`_ is specific to Doctrine and is basically the
     same as using an ``array``.
 
 .. code-block:: php
@@ -690,3 +690,4 @@ the relationship between the removed ``Tag`` and ``Task`` object.
 .. _`JSFiddle`: http://jsfiddle.net/847Kf/4/
 .. _`@a2lix/symfony-collection`: https://github.com/a2lix/symfony-collection
 .. _`symfony-collection`: https://github.com/ninsuo/symfony-collection
+.. _`ArrayCollection`: https://www.doctrine-project.org/projects/doctrine-collections/en/1.6/index.html