add update mechanism

This is some nice code found on stack overflow that I have been using
for a while that seems very reliable.  I just commented out a few
things since we really only want to check if it needs an update or if
it is already up to date.

advanced/Scripts/updatePihole

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Pi-hole: A black hole for Internet advertisements
+# (c) 2015, 2016 by Jacob Salmela
+# Network-wide ad blocking via your Raspberry Pi
+# http://pi-hole.net
+# Checks if Pi-hole needs updating and then
+#
+# Pi-hole is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+
+# Taken from http://stackoverflow.com/questions/3258243/check-if-pull-needed-in-git
+
+# Move into the git directory
+cd /etc/.pihole/
+
+LOCAL=$(git rev-parse @)
+REMOTE=$(git rev-parse @{u})
+BASE=$(git merge-base @ @{u})
+
+if [[ $LOCAL = $REMOTE ]]; then
+  echo "Up-to-date"
+elif [[ $LOCAL = $BASE ]]; then
+  echo "Updating Pi-hole..."
+  git pull
+elif [[ $REMOTE = $BASE ]]; then
+  : # Need to push, so do nothing
+else
+  : # Diverged, so do nothing
+fi