Add check for pacdiff and install pacman-contrib if not found

ArchUpdater.sh

@@ -22,6 +22,11 @@ if [ -z "$colordiff_installed" ]; then
     sudo pacman -S colordiff
 fi
 
+if [ -z $(which pacdiff) ]; then
+    echo "Installing pacman-contrib for the pacdiff step later, this will only run the first time you run this script"
+    sudo pacman -S pacman-contrib
+fi
+
 #Create list of -git packages from the aur
 gitlist=$(pacman -Qqm | grep git | grep -v debug)