Add instructions for serving on github.io

[seattleacademy]

I was quickly able to clone your code and use make to run on my development server. But for longer term support for derivative use with classes of students it would be helpful to given instructions (or a link to instructions) to serving through github.io as you do for your demo page.

Thanks for your fine work!

[seattleacademy]

I now realize that developed code can be served from the /docs folder either through GitHub pages or on a development server. Will close this issue, but a sentence explaining this may be beneficial in the README.MD file as this was not originally evident to me.