Add cross reference to role definitions

Author: astrojuanlu

doc/tutorial/narrative-documentation.rst

@@ -85,8 +85,9 @@ introduction paragraph in ``index.rst``:
 
    Check out the :doc:`usage` section for further information.
 
-The :rst:role:`doc` role you used automatically references a specific document
-in the project, in this case the ``usage.rst`` you created earlier.
+The :rst:role:`doc` :ref:`role <rst-roles-alt>` you used automatically
+references a specific document in the project, in this case the ``usage.rst``
+you created earlier.
 
 Alternatively, you can also add a cross-reference to an arbitrary part of the
 project. For that, you need to use the :rst:role:`ref` role, and add an