Add a note on DocumentType

Resources/doc/form_validation.rst

@@ -4,7 +4,11 @@ Form & Validation
 DocumentType
 ------------
 
-TODO
+This bundle provides a ``DocumentType`` to be used with the Symfony's Form
+component. As ``DocumentType`` extends the `EntityType`_ provided by Symfony's
+Doctrine bridge you can use all options available for the ORM users. The only
+difference is that ``DocumentType`` expects the ``DocumentManager`` name or
+instance passed with the ``document_manager`` option instead of ``em``.
 
 Unique constraint
 -----------------
@@ -17,4 +21,5 @@ The ``Unique`` constraint shares the same options as `UniqueEntity`_, which
 means that the ``em`` option should be used if you wish to specify the document
 manager explicitly instead of having it be inferred from the document class.
 
+.. _`EntityType`: https://symfony.com/doc/current/reference/forms/types/entity.html
 .. _`UniqueEntity`: http://symfony.com/doc/current/reference/constraints/UniqueEntity.html