docs: Update Debian docs with 'mopidyctl'

(cherry picked from commit 933cbe1dce)

docs/debian.rst

@@ -63,16 +63,16 @@ from a regular Mopidy setup you'll want to know about.
 - The init script runs Mopidy as the ``mopidy`` user. The ``mopidy`` user will
   need read access to any local music you want Mopidy to play.
 
-- To run Mopidy subcommands with the same arguments, and thus the same
-  configuration files, as the init script uses, you can use ``sudo service
-  mopidy run <subcommand>``. In other words, where you'll usually run::
+- To run Mopidy subcommands with the same user and config files as the init
+  script uses, you can use ``sudo mopidyctl <subcommand>``. In other words,
+  where you'll usually run::
 
       mopidy config
 
   You should instead run the following to inspect the system service's
   configuration::
 
-      sudo service mopidy run config
+      sudo mopidyctl config
 
   The same applies to scanning your local music collection. Where you'll
   normally run::
@@ -81,7 +81,12 @@ from a regular Mopidy setup you'll want to know about.
 
   You should instead run::
 
-      sudo service mopidy run local scan
+      sudo mopidyctl local scan
+
+  Previously, you used ``sudo service mopidy run <subcommand>`` instead of
+  ``mopidyctl``. This was deprecated in Debian package version 0.19.4-3 in
+  favor of ``mopidyctl``, which also work for systems using systemd instead of
+  sysvinit and traditional init scripts.
 
 - Mopidy is started, stopped, and restarted just like any other system
   service::