nixos: create 'modules/nixos' folder

Let's consolidate all modules under one path, so that NixOS,
home-manager, and nix-darwin (if I ever end up using it down the line)
would go under the same folder.

modules/nixos/hardware/ergodox/default.nix

@@ -0,0 +1,14 @@
+# ZSA keyboard udev rules
+{ config, lib, ... }:
+let
+  cfg = config.my.hardware.ergodox;
+in
+{
+  options.my.hardware.ergodox = with lib; {
+    enable = mkEnableOption "ZSA udev rules and user group configuration";
+  };
+
+  config = lib.mkIf cfg.enable {
+    hardware.keyboard.zsa.enable = true;
+  };
+}