Added steam

modules/system/programs/steam.nix

@@ -0,0 +1,16 @@
+{ config, lib, nixpkgs, ... }:
+
+{
+  nixpkgs.config.allowUnfree = true;
+  nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
+    "steam"
+    "steam-original"
+    "steam-run"
+  ];
+
+  programs.steam = {
+    enable = true;
+    remotePlay.openFirewall = true;
+    dedicatedServer.openFirewall = true;
+  };
+}