doc/user.rst: document the "filters" setting

doc/user.rst

@@ -425,9 +425,16 @@ The following table lists the audio_output options valid for all plugins:
        implement an external mixer :ref:`external_mixer`) or no mixer
        (:samp:`none`). By default, the hardware mixer is used for
        devices which support it, and none for the others.
+   * - **filters "name,...**"
+     - The specified configured filters are instantiated in the given
+       order.  Each filter name refers to a ``filter`` block, see
+       :ref:`config_filter`.
 
 More information can be found in the :ref:`output_plugins` reference.
 
+
+.. _config_filter:
+
 Configuring filters
 -------------------
 
@@ -442,6 +449,9 @@ To configure a filter, add a :code:`filter` block to :file:`mpd.conf`:
         name "software volume"
     }
 
+Configured filters may then be added to the ``filters`` setting of an
+``audio_output`` section, see :ref:`config_audio_output`.
+
 The following table lists the filter options valid for all plugins:
 
 .. list-table::