expand the help texts in admin or perhaps an overview of concepts doc

[davewhiteland]

The help texts in the admin are already nice, but could do with some expansion because they presuppose you know what the specific things are for -- it's tempting to think the help texts are good place for this because that's where you need them, but maybe this is really a missing document that could be linked from there.

Either way, some more clarification seems in order to help people setting up their own local MapIt.