elaborate in README

[ilka-schulz]

The README is extremely sparse.

Install qubes-dbus package

How? The package is neither in my AppVM or my dom0 package lists.

Make sure qubes-dbus-proxy is running

Where? In my AppVM or in dom0? How? Which command would I issue to make that sure?

Execute qui-domains in a shell.

Where? AppVM or dom0?

Also, some Information on what this repo contains would also be really nice. Tbh, the repo name does not speak for itself...