This is just to provide a brief usage example and note about sending
upstream messages with `react-native-fcm`

Android notification + data push notifications when the app is in the foreground only passes the data packet through, this changes it to pass the notification data too

In conforming with the method signatures as is the case with the
android version, I limited the arguments for `send()` to just
`senderId` and `payload`. This can still be improved upon by adding
`sendDataMessageSuccess` and `sendDataMessageFailure` to events being
fired across the bridge to Js.

* Fix iOS 10 specific documentation
* Fix typos/spelling-errors