docs: add setup instructions on first VM boot

[daPhipz]

There are missing instructions on how to install macOS VMs with Quickgui. Yes, there is https://github.com/wimpysworld/quickemu#macos-guest - but I can imagine that this is the last place where a "GUI-first" user will look for instructions.

I also think that adding SPICE setup instructions (See Ubuntu Guest) would be nice to show at first boot of the VM.

[ymauray]

Good call. Maybe a "help" screen in the app, on top of info in the README?

[PixsaOJ]

This issue is outdated, none of the link references are valid in OP's description