doc: explain audiogenerators/audiospec some more

doc/source/about.rst

@@ -40,6 +40,10 @@ action
   For example, ``{ 'kind': 'randomdir', 'paths': ['/my/dir', '/other/path'] }``
   will pick a random file from one of the two paths.
 
+  Its main atribute is ``kind``. The kind essentialy specifies the function that will be run among a
+  predefined set of :doc:`audiogenerators` . Every other attribute is an argument to the specified
+  audiogenerator.
+
 event
   An event is an alarm plus a list of actions. At given times, do those things
 

doc/source/install.rst

@@ -85,9 +85,12 @@ Events
 CONTINOUS_AUDIOSPEC
     when the playlist is too short, larigira picks something new. How? this is controlled by this variable.
     This variable should be set to the JSON representation of an audiospec describing how to generate new
-    audios. The default is ``{"kind": "mpd", "howmany": 1}``. You could, for example, change it to
-    ``{ "kind": "randomdir", "paths": ["/var/music"], "howmany": 10}``
-    or to ``{"kind": "mpd", "howmany": 5, "prefix": "background"}``.
+    audios. The default is ``{"kind": "mpd", "howmany": 1}``, which picks a random song from MPD library. You could, for example, change it to:
+
+    - ``{ "kind": "randomdir", "paths": ["/var/music"], "howmany": 5}`` to pick files from a specified
+       directory, ignoring MPD library completely. Here, ``howmany`` is set to 5 for performance sake
+    - ``{"kind": "mpd", "howmany": 10, "prefix": "background"}`` if you want to use the MPD library, but only
+       use one of its subdirectories. Please note that using ``mpd`` with a ``prefix`` can be slow, so this is setting ``howmany`` to 10 to gain some performance
 
     Yes, there's a typo in the name, but I'll keep it like this for compatibility
 EVENT_FILTERS