Add some minimal docs on Supervisor

needed a place to record how XML-RPC setup should go

docs/base/supervisor/setup.rst

@@ -0,0 +1,59 @@
+
+.. highlight:: sh
+
+=======
+ Setup
+=======
+
+Basic install of Supervisor itself::
+
+   sudo apt install supervisor
+
+
+Adding a Process [Group]
+========================
+
+TODO
+
+
+User Access
+===========
+
+By default only the ``root`` user can control Supervisor, e.g.::
+
+   sudo supervisorctl status
+
+TODO: describe how to give e.g. ``rattail`` user access as well
+
+
+Configuring XML-RPC
+===================
+
+Supervisor can provide a XML-RPC interface, with which Rattail can
+communicate "directly" instead of invoking shell commands.
+
+To enable this interface, create a file at
+e.g. ``/etc/supervisor/conf.d/supervisor.conf`` and in it put:
+
+.. code-block:: ini
+
+   [inet_http_server]
+   port = 127.0.0.1:8127
+   username = myuser
+   password = mypass
+
+Choose whichever credentials you like for the above; use the same ones
+in the remaining steps.
+
+Once the above file is in place, restart::
+
+   sudo systemctl restart supervisor
+
+Now within your Rattail config, set the Supervisor URL:
+
+.. code-block:: ini
+
+   [rattail]
+   supervisorctl_url = http://myuser:mypass@localhost:8127/RPC2
+
+You may need to restart the Rattail app(s) as well.