minor #1288 [WIP] Mention use of controller() function in docs (mablae)

This PR was squashed before being merged into the 1.3 branch (closes #1288).

Discussion
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[WIP] Mention use of controller() function in docs

This was discussed on twitter before:

https://twitter.com/lsmith/status/669145035770851328

Commits
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9c6b02d [WIP] Mention use of controller() function in docs

doc/providers/twig.rst

@@ -120,6 +120,15 @@ from a template:
     You must prepend the ``app.request.baseUrl`` to render calls to ensure
     that the render works when deployed into a sub-directory of the docroot.
 
+.. code-block:: jinja
+
+    {# You may also link to the controller directly without defining a route for it: #}
+    {{ render(controller(controller, attributes, query)) }}
+
+.. note::
+
+    Visit the symfony documentation for more information: http://symfony.com/doc/current/reference/twig_reference.html#controller
+
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