Update README to document APIs that have been deprecated or removed.
Update README to document APIs that have been deprecated or removed.

Change-Id: If5c0b76a4801607fb8cd976bb3ef5229135d25d4

mzimmerman/appengine,flowlo/appengine,skyeunknown084/appengine,flowlo/appengine,skyeunknown084/appengine,skyeunknown084/appengine,fuchsia-mirror/third_party-github.com-golang-appengine,flowlo/appengine,fuchsia-mirror/third_party-github.com-golang-appengine,mzimmerman/appengine,mzimmerman/appengine,golang/appengine,golang/appengine