Add information about how to use react-native-screens

[brentvatne]

• https://github.com/kmagiera/react-native-screens
• Explain why you would want to do this
• If people aren't using Expo, they need to follow the installation steps in the react-native-screens README
• If they are, all they need to do is:

import { useScreens } from 'react-native-screens';
useScreens();