docs: Add troubleshooting tips

docs/troubleshooting.rst

@@ -4,12 +4,55 @@
 Troubleshooting
 ***************
 
-TODO:
+If you run into problems with Mopidy, we usually hang around at ``#mopidy`` at
+`irc.freenode.net <http://freenode.net/>`_ and also have a `mailing list at
+Google Groups <https://groups.google.com/forum/?fromgroups=#!forum/mopidy>`_.
+If you stumble into a bug or got a feature request, please create an issue in
+the `issue tracker <https://github.com/mopidy/mopidy/issues>`_.
 
-- --show-config
-- --list-deps
-- SIGUSR1 for thread traceback logging
-- Issue tracker
-- Reporting bugs
-- Mailing list
-- IRC channel
+When you're debugging yourself or asking for help, there are some tools built
+into Mopidy that you should know about.
+
+
+Effective configuration
+=======================
+
+The command :option:`mopidy --show-config` will print your full effective
+configuration the way Mopidy sees it after all defaults and all config files
+have been merged into a single config document. Any secret values like
+passwords are masked out, so the output of the command should be safe to share
+with others for debugging.
+
+
+Installed dependencies
+======================
+
+The command :option:`mopidy --list-deps` will list the paths to and versions of
+any dependency Mopidy or the extensions might need to work. This is very useful
+data for checking that you're using the right versions, and that you're using
+the right installation if you have multiple installations of a dependency on
+your system.
+
+
+Debug logging
+=============
+
+If you run :option:`mopidy -v`, Mopidy will output debug log to stdout. If you
+run :option:`mopidy --save-debug-log`, it will save the debug log to the file
+``mopidy.log`` in the directory you ran the command from.
+
+If you want to turn on more or less logging for some component, see the
+docs for the :confval:`logging.levels/*` config section.
+
+
+Debugging deadlocks
+===================
+
+If Mopidy hangs without and obvious explanation, you can send the ``SIGUSR1``
+signal to the Mopidy process. If Mopidy's main thread is still responsive, it
+will log a traceback for each running thread, showing what the threads are
+currently doing. This is a very useful tool for understanding exactly how the
+system is deadlocking. If you have the ``pkill`` command installed, you can use
+this by simply running::
+
+    pkill -SIGUSR1 mopidy