Update librespot documentation

[Whhoesj]

The documentation about the setup of Spotify / librespot looks outdated. Looking through the code, it seems some options have been renamed and new ones have been added.

I've updated the documentation, I could open up a pull request for it if needed.

[pimseb]

Hello Could you tell me what i should change to make it work ? Snapcast crashes when I enable librespot in the config file

v 30 11:01:43 raspberrypi snapserver[2955]: (Salle_a_Manger)         stringValue: "video/ad"
Nov 30 11:01:43 raspberrypi snapserver[2955]: terminate called after throwing an instance of 'nlohmann::detail::type_error'
Nov 30 11:01:43 raspberrypi snapserver[2955]:   what():  [json.exception.type_error.305] cannot use operator[] with a string argument with string
Nov 30 11:01:43 raspberrypi snapserver[2955]: (Salle_a_Manger)         stringValue: "video/episode"
Nov 30 11:01:43 raspberrypi snapserver[2955]: (Salle_a_Manger)       }
Nov 30 11:01:43 raspberrypi snapserver[2955]: (Salle_a_Manger)       metadata {
Nov 30 11:01:43 raspberrypi snapserver[2955]: (Salle_a_Manger)         type: "tier1_port"
Nov 30 11:01:43 raspberrypi snapserver[2955]: (Salle_a_Manger)         metadata: "0"
Nov 30 11:01:43 raspberrypi snapserver[2955]: metadata: < "0">
Nov 30 11:01:43 raspberrypi systemd[1]: snapserver.service: Main process exited, code=killed, status=6/ABRT

Thank you