docs: add instructions for usage in an Expo project

[fobos531]

Summary

Adding on to this issue, I wondered why it was claimed that this package is not supported in an Expo project. Mainly due to the fact that the package doesn't require modification of any specific native project files so config plugins are not required. I went ahead to verify this by initializing an Expo project, adding this package and creating a development build of the app, and lo and behold, the package worked flawlessly. So, I would say, the only way this package is unsupported in Expo is by the fact that it doesn't have Expo installation instructions yet. This is what this PR does :)

Test Plan

N/A

What's required for testing (prerequisites)?

• expo project
• apple developer account for testing on a physical iOS device

What are the steps to reproduce (after prerequisites)?

• add this package by following the installation instructions provided in this PR
• use the package as usual.

Compatibility

OS	Implemented
iOS	✅
Android	✅

Checklist

• I have tested this on a device and a simulator
• I added the documentation in README.md
• I updated the typed files (TS and Flow)