Convert documentation to mdbooks

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
The current docs are based on sphinx, which I am unfamiliar with.

Describe the solution you'd like
I would prefer that we move the docs to mdbooks. I believe this would lower the bar for contributions.

Describe alternatives you've considered

Additional context

[MrPowers]

I created a proof of concept for the DataFusion Python documentation using mdBook: https://github.com/MrPowers/datafusion-book

The goal is to donate that repo / integrate the code into this repo.

Should I just move these mdBook docs into a branch of this repo?

[andygrove]

Could you create a PR to add this content to the repo? Maybe under docs/mdbooks ? We can then follow up with more PRs to add more content (and makes it easier for others to create PRs as well)