Deprecate this repository in favor of @amplitude/react-native

[andrewtremblay]

Now that @amplitude/react-native exists, it seems unneeded for this package to remain around. Unless there is a valid reason to continue to use this SDK for some users, having two SDKs can lead developers astray from the officially supported package.

I recommend that this github repo be archived, the npm package marked deprecated, and a message added to the readme telling others to use https://www.npmjs.com/package/@amplitude/react-native instead.

If there is still a valid use-case for this SDK, then a link to https://www.npmjs.com/package/@amplitude/react-native should still be provided, along with an explanation why this repo is still relevant.