docs: Make Raspbian audio settings system-wide
docs: Make Raspbian audio settings system-wide

Changing the audio output using raspi-config only changes it for the pi user. Mopidy as a service can't see that user-only config so make it a system-wide change.

Remove SD card expansion step, it is now automatic.
jodal/mopidy,kingosticks/mopidy,kingosticks/mopidy,mopidy/mopidy,jodal/mopidy,jcass77/mopidy,mopidy/mopidy,kingosticks/mopidy,jodal/mopidy,jcass77/mopidy,jcass77/mopidy,mopidy/mopidy