Add pkgbuild push script

update-pkgbuild.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+if ! git remote | grep -q ^aur$ ; then
+    git remote add aur ssh://aur@aur.archlinux.org/screencfg-git.git
+fi
+
+git subtree push --prefix pkg/arch/screencfg-git aur master
+
+git remote rm aur