[Feature]: Script which checks if the XDG vars are set on install

[iinsertNameHere]

Is your feature request related to a problem? Please describe:

112

Describe the solution you'd like:

A script which checks if the XDG vars are set on install. If not, it should walk the user through the process of setting them.

Additional context:

Nop

[yuki-was-taken]

I think this is unneeded. XDG_CURRENT_DESKTOP should be set by default, and most (if not all) DEs set it. However, WMs like Sway refuse to set it. (see my comment at #112) I'm in favour of putting a note in the documentation to tell users to manually set XDG_CURRENT_DESKTOP if the desktop stat returns "Unknown" for them.