Update Getting started instructions for React Native 0.63.2

[radazzouz]

Details

This PR updates the getting started instructions to work with React Native 0.63.2.

It also updates the CocoaPods integration to use the fat frameworks instead of the XCFrameworks, because of the known CocoaPods issues with XCFrameworks (CocoaPods/CocoaPods#9681 and CocoaPods/CocoaPods#9990)

Acceptance Criteria

• Create a new React Native project and integrate PSPDFKit using the new instructions.
• When approved, right before merging, rebase with master and increment the package version in package.json, package-lock.json, samples/Catalog/package.json, and samples/NativeCatalog/package.json (see example commit: 1bf805f).
• Create a new release (and tag) with the new package version (see https://github.com/PSPDFKit/react-native/releases).

[steviki]

LGTM!
Tested with integrating PSPDFKit into a new project.