Add osu module

Note that osu! is currently unfree since it depends on the bass audio
library.

configuration.nix

@@ -10,6 +10,7 @@
     ./modules/htop.nix
     ./modules/dual-function-keys.nix
     ./modules/tlp.nix
+    ./modules/osu
   ];
 
   boot.loader.systemd-boot.enable = true;

modules/osu/default.nix

@@ -0,0 +1,11 @@
+{ pkgs, lib, ... }:
+
+{
+  environment.systemPackages = with pkgs; [
+    osu-lazer-bin
+  ];
+
+  nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
+    "osu-lazer-bin"
+  ];
+}