docs: Update Expo CLI command, docs link and other improvements

[amandeepmittal]

Summary

Update Expo CLI command, docs link and other readability improvements to explain properties used in config plugin code snippet.

Motivation

Found that the command to install the library inside an Expo project referenced deprecated and removed Expo Global CLI. This PR updates the command to npx expo install ... since the latter refers to the latest Expo CLI, which doesn't require any global package installation.

Also:

• Updates the Expo docs link for the Stripe's React Native library reference
• Improve the readability around config plugin example

Documentation

Select one:

• I have added relevant documentation for my changes.
• This PR does not result in any developer-facing changes.

[cla-assistant]

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