xmonad: Allow to set brightness

modules/wm/xmonad/config.hs

@@ -48,6 +48,8 @@ myConfig = ewmhFullscreen $ ewmh $ Docks.docks $ def
   , ("M-b", sendMessage Docks.ToggleStruts)
   , ("M-p", spawn appLauncher)
   , ("M-i", spawn passLauncher)
+  , ("<XF86MonBrightnessDown>", spawn "xbacklight -dec 5")
+  , ("<XF86MonBrightnessUp>", spawn "xbacklight -inc 5")
   ]
   where
     appLauncher = "rofi -show combi -modes combi -combi-modes window,drun,run,ssh"

modules/wm/xmonad/default.nix

@@ -14,5 +14,8 @@
     };
   };
 
+  # control backlight
+  config.environment.systemPackages = [ pkgs.xorg.xbacklight ];
+
   config.systemd.services.upower.enable = true;
 }