Add documentation for missing tracks plugin

Also add link to the documentation plugin to the index

docs/plugins/index.rst

@@ -60,7 +60,8 @@ disabled by default, but you can turn them on as described above.
    convert
    info
    smartplaylist
-
+   missing
+   
 Autotagger Extensions
 ''''''''''''''''''''''
 
@@ -108,7 +109,8 @@ Miscellaneous
 * :doc:`convert`: Transcode music and embed album art while exporting to
   a different directory.
 * :doc:`info`: Print music files' tags to the console.
-
+* :doc:`missing`: List missing tracks.
+  
 .. _MPD: http://mpd.wikia.com/
 .. _MPD clients: http://mpd.wikia.com/wiki/Clients
 

docs/plugins/missing.rst

@@ -0,0 +1,71 @@
+Missing Plugin
+==============
+
+This plugin adds a new command, ``missing`` or ``miss``, which finds
+and lists, for every album in your collection, which tracks are
+missing. Listing missing files requires one network call to
+MusicBrainz.
+
+Installation
+------------
+
+Enable the plugin by putting ``missing`` on your ``plugins`` line in
+:doc:`config file </reference/config>`::
+
+    plugins:
+        missing
+        ...
+
+Configuration
+-------------
+
+The plugin accepts a single configuration directive, ``format``,
+either in your configuration file::
+
+    missing:
+        format: FMTSTR
+
+or in the command-line::
+
+    $ beet missing --help
+    Usage: beet missing [options]
+
+    Options:
+      -h, --help            show this help message and exit
+      -f FORMAT, --format=FORMAT
+                            print with custom FORMAT
+
+format
+~~~~~~
+
+The ``format`` option (default: ``None``) lets you specify a specific
+format with which to print every track. This uses the same template
+syntax as beets’ :doc:`path formats </reference/pathformat>`.  The usage
+is inspired by, and therefore similar to, the :ref:`list <list-cmd>`
+command.
+
+Examples
+-------------------------
+
+List all missing tracks in your collection::
+
+    beet missing
+
+List all missing tracks from 2008::
+
+    beet missing year:2008
+
+Print out a unicode histogram of the missing track years using `spark`_::
+
+    beet missing -f '$year' | spark
+    ▆▁▆█▄▇▇▄▇▇▁█▇▆▇▂▄█▁██▂█▁▁██▁█▂▇▆▂▇█▇▇█▆▆▇█▇█▇▆██▂▇
+
+
+TODO
+----
+
+- Add caching.
+ 
+--------------
+
+.. _spark: https://github.com/holman/spark