Update docs for easier integration with react-router using React Hooks

[imballinst]

Summary

This PR is a follow-up to #1976. Since react-router 5.1, there is an opportunity to make integration with this @elastic/eui easier -- with the use of useHistory.

You can see the sample repository here: https://github.com/Imballinst/elastic-react-router-hooks. I also added this link to the README should there are future users want to try it right away.

And for the GitHub pages of that app: https://imballinst.github.io/elastic-react-router-hooks/

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[chandlerprall]

Thank you very much for updating the routing documentation! The useHistory hook is definitely much more straight-forward to use. There are two changes I'd like to see, but I think your example is great (and seeing it in action at https://imballinst.github.io/elastic-react-router-hooks was a big help too.

Additionally, you'll need to sign our CLA (https://www.elastic.co/contributor-agreement) using the email address associated with your github account before we can accept this change.

[imballinst]

@chandlerprall I have adjusted the PR according to your requested changes and signed the CLA. Please take another look and feel free to let me know if there are nits. Thanks!

[chandlerprall]

Thanks again @imballinst for this update!