Created by: tobiasbueschel
Hi
I've noticed that the documentation for overriding CRA's default Jest configuration has gone out of sync with the actual implementation: https://github.com/facebook/create-react-app/blob/5e703a568a687dacdc45f1211355ce4b1b586625/packages/react-scripts/scripts/utils/createJestConfig.js#L75-L94
This PR fixes that!