lastgenre: Docs for blacklist feature

Author: JOJ0

docs/plugins/lastgenre.rst

@@ -161,6 +161,34 @@ genres remain, set ``whitelist: no``).
     If ``force`` is disabled the ``keep_existing`` option is simply ignored
     (since ``force: no`` means ``not touching`` existing tags anyway).
 
+Blacklisting Genres
+-------------------
+If you want to blacklist certain genres, they could simply be removed from the
+``whitelist``. This way, they will never be fetched from Last.fm. To only forbid them
+for a specific artist, the ``blacklist`` can be used. A possible ``blacklist`` file would
+look like this:
+
+.. code-block:: text
+
+    fracture:
+         ^(heavy|black|power|death)?\s?(metal|rock)$|\w+-metal\d*$
+        progressive metal
+    gilles peterson:
+        samba
+        bossa nova
+    *:
+        electronic
+
+A combination of regex patterns and plain genre names is possible. The ``*`` key matches
+all artists that are not explicitly defined, which is effectively the same as removing
+them from the whitelist (helpful if the default whitelist is desired to be kept).
+
+Set the ``blacklist`` option to the path of a blacklist file to enable this feature.
+
+.. attention::
+    Do not use single or double quotes around the genre names or regex patterns.
+
+
 Configuration
 -------------
 
@@ -201,7 +229,11 @@ file. The available options are:
   last.fm tags were fetched for tracks, albums and artists. This is done before
   any canonicalization and whitelist filtering is applied. It's useful for
   tuning the plugin's settings and understanding how it works, but it can be
-  quite verbose. Default: ``no``.
+  quite verbose.
+  Default: ``no``.
+- **blacklist**: The path to a blacklist file that contains genres to exclude from being
+  set as genres for specific artists. See `Blacklisting Genres`_ for more details.
+  Default: ``no``.
 
 Running Manually
 ----------------