add documentation for play importer prompt choice

docs/plugins/play.rst

@@ -4,8 +4,8 @@ Play Plugin
 The ``play`` plugin allows you to pass the results of a query to a music
 player in the form of an m3u playlist or paths on the command line.
 
-Usage
------
+Command Line Usage
+------------------
 
 To use the ``play`` plugin, enable it in your configuration (see
 :ref:`using-plugins`). Then use it by invoking the ``beet play`` command with
@@ -29,6 +29,18 @@ would on the command-line)::
 While playing you'll be able to interact with the player if it is a
 command-line oriented, and you'll get its output in real time.
 
+Interactive Usage
+-----------------
+
+The `play` plugin can also be invoked during an import. If enabled, the plugin
+adds a `plaY` option to the prompt, so pressing `y` will execute the configured
+command and play the items currently being imported.
+
+Once you exit your configured player, you will be returned to the import
+decision prompt.  If your player is configured to run in the background (in a
+client/server setup), the music will play until you choose to stop it, and the
+import operation continues immediately.
+
 Configuration
 -------------