TRACKING: Follow-up to black transition

[neiljp]

• [x] Add black 'badge' to README
• [x] Document basic expected style (isort + black?)
• [ ] Document auto-fixing code at base level & editor integration
• [ ] Pre-commit hook?
• [ ] Migrate to zulint (may require updates to earlier categories)
• [ ] Consider deprecation of flake8 settings, use of autopep8, use of autoflake; use of pyflakes?

[andersk]

• [x] Consider applying Black to setup.py and tools/*, which were initially excluded (discussion).

[neiljp]

#1192 resolves second point.

[neiljp]

Marking flake8 settings and similar as completed, since we have migrated to ruff.