Add a note about React/React-Native versioning
Add a note about React/React-Native versioning

Summary:
I'm adding a readme inside the ./Libraries/Renderer folder
to explain how React and React Native are aligned.

Changelog:
[Internal] [Changed] - Add a note about React/React-Native versioning

Reviewed By: cipolleschi

Differential Revision: D36445819

fbshipit-source-id: cf1b071b9996bcc8222deab2e9458f014766f2a9

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