Improve style prop display

Summary:
- Display the description when it exists
- Display the platform

<img width="667" alt="screen shot 2016-01-24 at 1 37 45 pm" src="https://cloud.githubusercontent.com/assets/197597/12539106/fb226d08-c29f-11e5-83ad-f85bb42ed693.png">
Closes https://github.com/facebook/react-native/pull/5520

Reviewed By: svcscm

Differential Revision: D2859743

Pulled By: vjeux

fb-gh-sync-id: 0ccfeca7bbdfa837501378c0bf701d589fea48d8