docs: Add info about PulseAudio when running as a service
docs: Add info about PulseAudio when running as a service

When using PulseAudio and running Mopidy as a service, some
configuration has to be added for this. This documents what you have to
do.

The setup is based on these:
https://wiki.archlinux.org/index.php/PulseAudio/Examples#PulseAudio_over_network
https://github.com/mopidy/mopidy/issues/954#issuecomment-73369712

vrs01/mopidy,tkem/mopidy,jcass77/mopidy,mopidy/mopidy,mopidy/mopidy,jcass77/mopidy,tkem/mopidy,ZenithDK/mopidy,jodal/mopidy,tkem/mopidy,adamcik/mopidy,kingosticks/mopidy,adamcik/mopidy,mokieyue/mopidy,mokieyue/mopidy,ZenithDK/mopidy,vrs01/mopidy,vrs01/mopidy,ZenithDK/mopidy,adamcik/mopidy,kingosticks/mopidy,mopidy/mopidy,kingosticks/mopidy,jodal/mopidy,jcass77/mopidy,vrs01/mopidy,tkem/mopidy,mokieyue/mopidy,jodal/mopidy,ZenithDK/mopidy,mokieyue/mopidy