[#2459] Adding notes about new autoescape feature

Author: weaverryan

reference/configuration/twig.rst

@@ -32,6 +32,9 @@ TwigBundle Configuration Reference
                     type:                 ~
                     value:                ~
             autoescape:                ~
+
+            # The following were added in Symfony 2.3.
+            # See http://twig.sensiolabs.org/doc/recipes.html#using-the-template-name-to-set-the-default-escaping-strategy
             autoescape_service:        ~ # Example: @my_service
             autoescape_service_method: ~ # use in combination with autoescape_service option
             base_template_class:       ~ # Example: Twig_Template