Inform users they have updated to a new major version

[jamiewade]

At the moment, running sh update.sh just pulls down the latest code changes.

It would be great if PieBot was aware of the current major version number that instance is running (1.x, 2.x, 3.x etc), and if an update is run that is a different major version number, the user is notified so they can make the necessary config changes to support the new version.