Add Transfer API Endpoint Search Example to docs

[sirosen]

Based off of #253, I think it would be nice to have another advanced TransferClient usage example focusing on endpoint_search()

I don't want to be re-documenting the API behaviors, but rather showing how you can use the iterable results to get more sophisticated behavior. Something along these lines:

• Create three endpoints with content in their Keywords, Organization, and Department fields
• Perform searches which capture cross-sections of these endpoints
• Show a search which captures two of them "accidentally" (e.g. Organization for EP1 and Keywords for EP2 both have the same content)
• Show how to check fields for stricter matching client-side to fix the prior search (capture EPs with overlapping fields, then explicitly check that Organization=X)