Update README to reflect that appengine/image has been ported.
Update README to reflect that appengine/image has been ported.

Change-Id: I8d058b2f64696959896534b2e01ba575684e43a9

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