Update to README documentation for issue #798

Refers to the use of /api/ at the beginning of sample routes to match the use of `prefix :api` in sample code.
I am nitpicking, but lets not include this comment. We would want to explain just about everything otherwise, like "what's format :json" ... this is just an example, and the doc is pretty clear below.

The other change totally makes sense since that's just wrong right now.