Document recommendations for headless setups

[jodal]

• [x] Use case: Run Mopidy-MPRIS + Rygel on a headless system to support playing audio in Mopidy from an UPnP client.
• [ ] Research: Does any MPRIS clients support using the system bus?
• [ ] Research: Can we start a session bus if there's none? Ref. wrap-dbus script. Will Rygel running as some other user on the system be able to connect to Mopidy-MPRIS using the mopidy user's session bus?

[kmiterror]

I have a headless setup with rygel working. You need some fake x server to have dbus working with mpris. I use xvfb, it's available in most repos. I start it with a command:

Xvfb :1 -screen 0 1x1x8 &

It creates a minimal x server 1x1 pixel 8bits color, so it has minimal memory impact and enable mopidy-mpris and rygel to work through dbus.

Ofcourse DISPLAY envirnoment variable needs to be set up, I'm setting it in /etc/enviroment to:

DISPLAY=:1

Im running it that way for few months.