Add react example code to the README

[IanPhilips]

Submitting this is a talking point, feel free to suggest another way of adding this documentation.

I had to load using the CDN because of #181.

[binarykitchen]

Thanks for this!

Honestly I am not a fan of using CDN. Understand it's a limitation due to Gatsby being a SSR. That would mean your example is actually for Gatsby itself, not React. Because in a normal client-side React app we wouldn't have this problem.

Submitted a review.

[IanPhilips]

Good point! Thanks for the review, I'll fix those issues.

This is definitely a Gatsby example. I can cook up a react example, would you prefer to have the gatsby example on file somewhere or just a plain react example?

[binarykitchen]

Thanks. Plain React please.