The previous commit didn't actually work, and I shouldn't need to
change the variables often, so it's much simpler to not have them.
In the event that I do need to change something, rg and sd should get
the job done well.
This is a working example of using the modules in our existing
configuration to start a network of virtual machines with
nixos-build-vms. Note that VMs take longer to start up in this case than
nixos-rebuild build-vm, and that said VMs may lack certain functionality
(such as dynamic resolution in GNOME) that would otherwise be present
with build-vm.
Although networks are certainly cute (and I'm glad that I feel familiar
with them thanks to my better understanding of Nix), they do seem less
convenient than nixos-rebuild build-vm and don't appear to support Nix
flakes. Networks therefore seem more useful for running multiple one-off
services that couldn't otherwise be ran in a container.
