Add react guide

[simondel]

This guide is meant to help users who want to use Stryker with a React project.

[simondel]

@mthmulders @Archcry @JoshuaKGoldberg Could you provide some feedback on this guide?

Right now, I have an npm i -D command in the guide. We may want to replace this with yarn for the React example but I'm not sure.

[nicojs]

I would like to propose a different directory structure. Let's put this guide under stryker/configuration/react.md. Grouping all configuration guides together would make scraping easier. We'll update the guides for scraping later, but let's at least make sure the location is already what we want it to be.

[simondel]

I'll fix the layout of the repo in a separate commit directly to master.

[nicojs]

Great job! Thanks

[mthmulders]

A bit late to the party, but it looks good to me!

[nicojs]

You, my friend, are always right on time for any party.