Publish docs as mdbook

We have an automation that allows building docs as mdbook while keeping it versioned.

An example can be found here:
book: https://github.com/matter-labs/zksync-os-server/tree/main/docs
CI: https://github.com/matter-labs/zksync-os-server/blob/main/.github/workflows/deploy-docs.yml

We need to make it work the same way here and mention the book in the readme.