Document how to add a new music source to the Strix Music App

[Arlodotexe]

Background

With the new top-level app infrastructure, we'll be able to start adding music sources at a much faster rate.

The problem

Since this is all new, there are no guides or documentation on how to do this.

The solution

Write documentation for how to add a new Music Source to the Strix Music App.

[Arlodotexe]

Since I'm already adding OneDrive support back into the new app architecture, I'll use that to document the process.