init nix-os configuraion files

modules/nixos/virtualize/virtualbox.nix

@@ -0,0 +1,15 @@
+{ config, pkgs, lib, ... }: 
+{
+  config = {
+    # Enable virtualbox
+    # Ref: https://nixos.wiki/wiki/Virtualbox
+    #virtualisation.virtualbox.host.enable = true;
+    #virtualisation.virtualbox.host.enableExtensionPack = true; //NOTE: this is unfree
+    #users.extraGroups.vboxusers.members = [ config.owner ];
+
+    environment.systemPackages = with pkgs; [
+      #linuxPackages_latest.virtualboxGuestAdditions
+    ];
+
+  };
+}