Document Goto plugin upgrade

1) Document how the configuration works/is structured and
2) Document on how to upgrade from 7.5 to 7.6

Part 2 should be part of the existing upgrade documentation for 7.6

Note: we do not want the upgrader of 7.5 to 7.6 to take care of the upgrade. This is very important piece of configuration. Developers need to be aware where this is configured.