Update search location of serializer configuration

Author: robob4him

serializer.rst

@@ -137,6 +137,8 @@ In addition to the ``@Groups`` annotation, the Serializer component also
 supports YAML or XML files. These files are automatically loaded when being
 stored in one of the following locations:
 
+* All ``*.yaml`` and ``*.xml`` files in the ``config/serializer/``
+  directory.
 * The ``serialization.yaml`` or ``serialization.xml`` file in
   the ``Resources/config/`` directory of a bundle;
 * All ``*.yaml`` and ``*.xml`` files in the ``Resources/config/serialization/``