Add defaultSettings's type to documentation (#716)

Include a better description of the expected value on the `defaultSettings` prop.

Author: luisfmsouza

README.md

@@ -114,7 +114,7 @@ You must pass at least the `writeKey`. Additional configuration options are list
 | `maxBatchSize`             | 1000      | How many events to send to the API at once                                                                                                     |
 | `trackAppLifecycleEvents`  | false     | Enable automatic tracking for [app lifecycle events](https://segment.com/docs/connections/spec/mobile/#lifecycle-events): application installed, opened, updated, backgrounded) |
 | `trackDeepLinks`           | false     | Enable automatic tracking for when the user opens the app via a deep link (Note: Requires additional setup on iOS, [see instructions](#ios-deep-link-tracking-setup))                                                            |
-| `defaultSettings`          | undefined | Settings that will be used if the request to get the settings from Segment fails                                                               |
+| `defaultSettings`          | undefined | Settings that will be used if the request to get the settings from Segment fails. Type: [SegmentAPISettings](https://github.com/segmentio/analytics-react-native/blob/master/packages/core/src/types.ts#L291)                                                               |
 | `autoAddSegmentDestination`| true      | Set to false to skip adding the SegmentDestination plugin                                                                                      |
 | `storePersistor`           | undefined | A custom persistor for the store that `analytics-react-native` leverages. Must match `Persistor` interface exported from [sovran-react-native](https://github.com/segmentio/sovran-react-native).|
 | `proxy`                    | undefined | `proxy` is a batch url to post to instead of 'https://api.segment.io/v1/b'.                                                                    |