feat(void): add brightness control keybinds

void.nix

@@ -1,7 +1,7 @@
 # Edit this configuration file to define what should be installed on
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
-{ config, ... }:
+{ config, pkgs, ... }:
 {
   imports = [
     ./hardware-configuration-void.nix
@@ -46,4 +46,9 @@
   ];
   boot.kernelModules = ["i2c-dev" "ddcci_backlight"];
   hardware.i2c.enable = true;
+
+  # package for controlling brightness on external monitor
+  environment.systemPackages = [
+    pkgs.ddcutil
+  ];
 }