Merge PR #1374 into develop

Differences from the original PR:

- Squashed commits.
- Reworded commit summary.
- No comma after `e.g.`.
- Wrapped lines in the commit message.
- Fixed python-mpd2 link.

Closes #1374

powerline/segments/common/players.py

@@ -208,7 +208,14 @@ class MpdPlayerSegment(PlayerSegment):
 mpd = with_docstring(MpdPlayerSegment(),
 ('''Return Music Player Daemon information
 
-Requires mpc command to be acessible from $PATH or ``mpd`` Python module.
+Requires ``mpd`` Python module (e.g. |python-mpd2|_ or |python-mpd|_ Python
+package) or alternatively the ``mpc`` command to be acessible from $PATH.
+
+.. |python-mpd| replace:: ``python-mpd``
+.. _python-mpd: https://pypi.python.org/pypi/python-mpd
+
+.. |python-mpd2| replace:: ``python-mpd2``
+.. _python-mpd2: https://pypi.python.org/pypi/python-mpd2
 
 {0}
 :param str host: