Set up platform for documentation

[erciccione]

There are multiple options, like readthedocs or mdbook.

[erciccione]

This is in progress and almost completed: https://github.com/haveno-dex/haveno-docs

Pull requests:

• https://github.com/haveno-dex/haveno/pull/456
• https://github.com/haveno-dex/haveno-ts/pull/141
• https://github.com/haveno-dex/haveno-site/pull/86