ADD external brighntess controller

dot_bin/executable_xbrightness

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# control external monitor brightness using ddc/ci
+
+level="$1"
+
+if [ $level -lt 0 ] || [ $level -gt 100 ]; then
+    echo "brightness must be between 0 and 100"
+    exit 1
+fi
+
+dpys=$(ddcutil detect --async | grep Display | cut -f2 -d' ' | tr '\n' ' ')
+
+# NOTE: as nice as it would be, it seems that I can't run all of these in
+# parallel since ddc will get confused (idk why)
+for d in $dpys; do
+    ddcutil setvcp 10 "$level" -d "$d" > /dev/null
+done
+
+wait
+