Comment unsupported `flex` prop
Comment unsupported `flex` prop

Summary:
Changelog:
[Internal] - Add comment on `flex` prop for visibility

Reviewed By: Andrey-Mishanin

Differential Revision: D39383844

fbshipit-source-id: 0fc64a2dd04a8ab0099389e7e5c49ee5816ba01f

facebook/react-native,javache/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,javache/react-native,facebook/react-native,javache/react-native,javache/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,janicduplessis/react-native,janicduplessis/react-native