Add high level discussion on ways to get data in and out of Grouper

from Shilen Patel: Before talking specifically about the loader, I wonder if there should be a section that (at a high level) talks about the ways to get data into Grouper. There are many methods and it seems like it could be confusing to know what they all are and when you use each. So maybe just stating the options and linking to their wiki pages may be useful. Loader, WS, API, GSH, Messaging, manual changes via UI, anything else?

from Carey Black: grouper client? ( Technically a Web Service wrapper, but a thing to talk about as a method too. )