Add usage information to README

Author: valrus

README.md

@@ -1,9 +1,20 @@
 # alfred-mpd
 
-*Copyright 2016 Ian McCowan*  
-
 alfred-mpd is an [Alfred](http://www.alfredapp.com/) workflow designed to make
 playing music using [mpd](https://www.musicpd.org) extremely quick and convenient.
 
 This workflow uses the [python-mpd2](https://github.com/Mic92/python-mpd2) library
-to control mpd from Python.
+to control mpd from Python. (The library is included; you don't need to install
+it yourself. This is just to give credit.)
+
+Current functionality is designed around the way I myself play music, which is to
+say, a whole album at a time. In the future I may be willing to implement other
+use cases if people ask, but I get the impression that use of mpd on a Mac is
+at best an extremely niche proposition.
+
+Trigger this workflow using the `mpdalbum` keyword. Alfred will scan your mpd
+database, and you can use Alfred's fuzzy matching to search for an album and
+play it. The workflow also comes with a hotkey (default ⌃⇧↑) to save you
+from having to type the keyword. You may of course change or disable it.
+
+*Copyright 2016 Ian McCowan*