Docs: Add example with new React Router

[silvenon]

Also, keep #157 in mind.

[camerongreen]

Just want to 👍 this! I'm just learning react and this is a bit of a stumbling block for me using this library. Might revisit when I've upped my react understanding a bit.

[camerongreen]

I did one more search before I gave up and got it working with this, https://codesandbox.io/s/6l1li?file=/src/index.tsx

[silvenon]

Oh, cool, thanks for the demo!