changed documentation for accessibilityHint
changed documentation for accessibilityHint

Summary:
Changed documentation for accessibility Hint so that its no longer only available on iOS

Also added full description of documentation for accessibility Role as it was missing earlier

Reviewed By: PeteTheHeat

Differential Revision: D9072572

fbshipit-source-id: c8d20f30df588717d9ec37721c2aa3c86a0664c6

javache/react-native,facebook/react-native,myntra/react-native,hammerandchisel/react-native,hoangpham95/react-native,janicduplessis/react-native,hammerandchisel/react-native,facebook/react-native,exponent/react-native,hoangpham95/react-native,pandiaraj44/react-native,hoangpham95/react-native,arthuralee/react-native,pandiaraj44/react-native,facebook/react-native,exponent/react-native,exponentjs/react-native,exponent/react-native,facebook/react-native,javache/react-native,javache/react-native,javache/react-native,exponentjs/react-native,facebook/react-native,pandiaraj44/react-native,hoangpham95/react-native,exponent/react-native,janicduplessis/react-native,janicduplessis/react-native,myntra/react-native,hoangpham95/react-native,myntra/react-native,facebook/react-native,pandiaraj44/react-native,hammerandchisel/react-native,hoangpham95/react-native,janicduplessis/react-native,javache/react-native,myntra/react-native,hammerandchisel/react-native,hoangpham95/react-native,javache/react-native,hammerandchisel/react-native,hammerandchisel/react-native,exponent/react-native,arthuralee/react-native,exponent/react-native,myntra/react-native,pandiaraj44/react-native,myntra/react-native,arthuralee/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,hammerandchisel/react-native,facebook/react-native,exponentjs/react-native,myntra/react-native,exponentjs/react-native,myntra/react-native,exponentjs/react-native,exponent/react-native,arthuralee/react-native,janicduplessis/react-native,arthuralee/react-native,hammerandchisel/react-native,pandiaraj44/react-native,javache/react-native,myntra/react-native,pandiaraj44/react-native,pandiaraj44/react-native,exponentjs/react-native,janicduplessis/react-native,hoangpham95/react-native,facebook/react-native,javache/react-native,exponentjs/react-native,exponent/react-native,janicduplessis/react-native,exponentjs/react-native