Improve viewing experience on mobile

[aszenz]

Reading documentation on mobile isn't a pleasant experience for these reasons:

• The navigation sidebar cannot be hidden away it eats up a lot of space

• The text is way too small, you have to zoom in

Basically make the docs website responsive.

Instead of trying to reinvent custom navigation and styles maybe use
https://docusaurus.io/, it provides a lot of features for free and users are used to navigating such sites.