Add react app boilerplate

Add react app boilerplate

This content was created automatically by running the following
command in an empty directory:

	npx create-react-app puzzless

and then copying all of the files created (other than
package-lock.json) in the puzzless directory into the current
directory.

Apparently the creete-react-app code comes from:

	https://github.com/facebook/create-react-app

but I have no idea which version was actually used here.

Apparently this sample react app can be started by running either of
the following commands:

	npm start

or:

        yarn start

And then pointing a browser at localhost:3000 (which apparently the
above commands also do?).