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/system/packages/default.nix

@@ -0,0 +1,35 @@
+# Common packages
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.my.system.packages;
+in
+{
+  options.my.system.packages = with lib; {
+    enable = my.mkDisableOption "packages configuration";
+
+    allowAliases = mkEnableOption "allow package aliases";
+
+    allowUnfree = my.mkDisableOption "allow unfree packages";
+  };
+
+  config = lib.mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [
+      vim
+      wget
+    ];
+
+    programs = {
+      vim.defaultEditor = true; # Modal editing is life
+
+      zsh = {
+        enable = true; # Use integrations
+        # Disable global compinit when a user config exists
+        enableGlobalCompInit = !config.my.home.zsh.enable;
+      };
+    };
+
+    nixpkgs.config = {
+      inherit (cfg) allowAliases allowUnfree;
+    };
+  };
+}