2023 04 16 small branch naming fixes

[roterski]

Hello! :wave:

I've recently discovered this project and in process of evaluating it for my needs (vs polylith or vanilla deps.edn) found few easy to fix issues:

• bb test-upstream was failing because default branch test was expecting master not main,
• code links in API.md docs didn't work because they pointed to develop branch which is not visible here.

Cheers! 🙌