bluetooth documentation

[barrelltitor]

Added the bluetooth documentation, let me know what should be changed in it!

[GioF71]

Hello, thank you for the great contribution.
There are not many changes I would do, I will ask you. Would it be ok if I open issues on your repo?
I can anticipate I would avoid to define the "default" card in ~/.asound.conf and then use aplay to the default card. I would instead create a named card and try to play to that with aplay.
Anyway we talk about very minor things.
Also markdown synthax but I can fix that myself.

Thank you again.

[barrelltitor]

Just turned on issues on the fork. For testing yeah using aplay on a named card might be better to not forget it on the host, will look into that!

Thanks for fixing the markdown issues, I'm not very good with that yet