Document maintaining a fork of react-scripts as an alternative to ejecting

Created by: gaearon

It is not common knowledge that you can fork react-scripts, publish your fork, and then do create-react-app my-app --scripts-version my-react-scripts-fork.

This can be useful for customized setups, especially if you want to merge upstream updates once in a while. And with something like https://github.com/1egoman/backstroke, it might not even be painful!