Add description in package.json for react-native-flipper (#1055)

Summary:
There's `TODO` in the description for `react-native-flipper` so this should be updated

## Changelog

Internal change.
Pull Request resolved: https://github.com/facebook/flipper/pull/1055

Test Plan: No test plan required.

Reviewed By: mweststrate

Differential Revision: D21256140

Pulled By: passy

fbshipit-source-id: 6b07e38b80ac395481270b05fca6823ec6559da5

react-native/react-native-flipper/package.json

@@ -2,7 +2,7 @@
   "name": "react-native-flipper",
   "title": "React Native Flipper Bindings",
   "version": "0.39.0",
-  "description": "TODO",
+  "description": "Flipper bindings for React Native",
   "main": "index.js",
   "types": "index.d.ts",
   "scripts": {