Provide base campaign segments (or just good docs) by user journey

[aschweigert]

Asana: https://app.asana.com/0/1200942827698993/1201001433518149/f
Details: https://docs.google.com/document/d/1yaRwAQirSrCyNdjqlyGdeALLwrNfrJEkZsKvwM66e_w/edit#heading=h.wzhi18vbtekt

Documentation would help triage this issue, but I think having some default segments would be a better way to go.

I generally agree with the basic set of segments Brian outlined in the doc:

Donors
Frequent readers
Newsletter subscribers
Referred by [Smartnews, or another aggregator, etc.]
Everyone else

We should make sure we have a solid understanding of who would fall into these segments and then build at least a few default segments directly into the plugin and think about how best to guide new publishers to setting these up in a way that will work well in most cases.