Technical doc for smoother contribution

[AMK9978]

Is this related to a problem? Please describe.

I'm new to black in terms of contribution. I'd like to work on this issue #4353, but I'm struggling to understand the basics of data structures and the flow of black. I searched the black's website and GitHub issues but didn't find something useful for this issue.

Describe the solution you'd like

I'd like to have a technical document explaining the logic of black.

Describe alternatives you've considered

Additional context

I had to read previous pull requests to get a clue about modifying black. Technical docs can ease contribution.