Publish the working demo on github.io

[Juergen Gutsch]

Is your feature request related to a problem? Please describe.
I'm missing a working demo somewhere online

Describe the solution you'd like
As a developer, I'd like to see a working demo in the browser before cloning the repo

Describe alternatives you've considered
What about an online working demo at stone_css.github.io?
It's all on GitHub then and easy to maintain.

Additional context
n/a

[Emanuele Bartolesi]

I have updated the readme and I published a demo here: https://kasuken.github.io/stone.css/