Add to installation guide - How to upgrade Mailscanner

[Tristan Rhodes]

I have read a lot about Julian's nifty upgrade process and the way it handles configuration files.

I think there should be a blurb on the "Installation Guide" about how to upgrade Mailscanner and what will happen to the configuration files.  (Always a good idea to proclaim your cool features.  This may cause more admins to choose Mailscanner)

I'm still not sure how to upgrade, but I think I just need to download the new file, untar it and run install.sh again, correct?  

Thanks,

Tristan Rhodes