Increase step for luminosity setup

And use a constant to make commands consistent.

Install/Templates/i3/config

@@ -40,8 +40,9 @@ bindsym XF86AudioLowerVolume exec --no-startup-id amixer set Master unmute 2dB-
 bindsym XF86AudioMute exec --no-startup-id amixer set Master unmute 0
 
 # adjust luminosity
-bindsym XF86MonBrightnessUp exec --no-startup-id xbacklight + 2
-bindsym XF86MonBrightnessDown exec --no-startup-id xbacklight - 2
+set $lum_step 5
+bindsym XF86MonBrightnessUp exec --no-startup-id xbacklight -inc $lum_step
+bindsym XF86MonBrightnessDown exec --no-startup-id xbacklight -dec $lum_step
 
 # change focus
 bindsym $mod+$left focus left