Fix README typo.
Fix README typo.

Change-Id: I74640d13c123c35e7e6ab00343d8e98567df2249

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