Fix cross-linking

Author: Márk Sági-Kazár

clients/includes/install-message-factory.inc

@@ -6,9 +6,9 @@ to install one as well (for example `Guzzle PSR-7`_):
     $ composer require guzzlehttp/psr7
 
 In order to provide full interoperability, message implementations are
-accessed through :ref:`factories <message-factory>`. Message factories for
+accessed through :doc:`factories </message/message-factory>`. Message factories for
 `Diactoros`_ and `Guzzle PSR-7`_ are available in the
-:ref:`message <message>` component:
+:doc:`message </message>` component:
 
 .. code-block:: bash