Add an example with Create React App that includes React router

[tyrw]

Currently it's pretty easy to use the guide to set up a very basic React app with AnyMod using the Guide https://guide.anymod.com/guide/react.html.

However when there is a router involved, it can get more complicated to know where to put AnyMod.render(). Since there are already lots of tutorials for CRA, we could add an example that starts at the end of one of the CRA tutorials and then adds mods to a few different routes. That would help users who are working in more complex React apps.