Add example vr flake thingy (not yet included)

vr.nix

@@ -0,0 +1,15 @@
+{
+  inputs = {
+    nixpkgs-xr.url = "github:nix-community/nixpkgs-xr";
+  };
+
+  outputs = { nixpkgs, nixpkgs-xr, ... }: {
+    nixosConfigurations.foo = nixpkgs.lib.nixosSystem {
+      # ...
+      modules = [
+        # ...
+        nixpkgs-xr.nixosModules.nixpkgs-xr
+      ];
+    };
+  };
+}