meta: Add network example

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.

modules/default.nix

@@ -10,5 +10,12 @@
     ./starship.nix
     ./stylix.nix
     ./thunar.nix
+    ./user.nix
   ];
+
+  virtualisation.vmVariant = {
+    imports = [
+      ./virtualization.nix
+    ];
+  };
 }

modules/user.nix

@@ -0,0 +1,12 @@
+let VARIABLES = import ../src/variables.nix; in {
+  users = {
+    mutableUsers = false;
+
+    users."${VARIABLES.username}" = {
+      isNormalUser = true;
+      uid = 1000;
+      password = "user";
+      extraGroups = [ "wheel" "networkmanager" ];
+    };
+  };
+}

modules/virtualization.nix

@@ -0,0 +1,17 @@
+{
+  virtualisation = {
+    memorySize = 8192;
+    cores = 4;
+  };
+
+  virtualisation.qemu.options = [
+    "-device virtio-vga-gl"
+    "-display sdl,gl=on,show-cursor=off"
+    "-full-screen"
+    "-audio pa,model=hda"
+  ];
+
+  environment.sessionVariables = {
+    WLR_NO_HARDWARE_CURSORS = "1";
+  };
+}