Add update script so I don't have to copy-paste from the readme every time

scripts/gpd-script-update

@@ -0,0 +1,12 @@
+#! /usr/bin/bash
+
+if [ -z $(which git 2>/dev/null) ]; then
+  printf "\n$(tput setaf 1)-- We didn't find git! Is it installed? --$(tput sgr0)\n\n"
+  printf "On Ubuntu and similar distros, git can be installed with the following command:\n"
+  printf "  $(tput setaf 2)sudo apt install git$(tput sgr0)\n\n"
+  printf "Please try again after installing git.\n\n"
+else
+  cd ~/.local/gpd-win3
+  git pull
+  cd -
+fi