Update the React Native Datastore getting started page

**Is your feature request related to a problem? Please describe.**
The getting started page for Datastore is confusing and needs updates:

- The library is requested to be installed twice.
- The SQL Lite adapter is mentioned without any context on why it is helpful.
- Configuring Amplify is not mentioned in the getting started page at all.

https://docs.amplify.aws/lib/datastore/getting-started/q/platform/react-native/

**Describe the solution you'd like**

- Clarify the path with the initial set up for Datastore