I spent a LOT of time working with beginner programmers and saw many examples of learners finding their way into documentation and sources of information that were unhelpful, intimidating or not intended for them. Chaos, confusion and disappointment would ensue and this would take a significant amount of time and effort to undo. https://codewith.mu/ and https://madewith.mu/ are both websites for the target users of beginner programmers or those teaching coding (Python).
Mu's developer docs are in the "usual place" for Python projects (mu.rtfd.io) and I hope they make sense to any experienced developer.
https://codewith.mu/en/developers
Which links to here:
https://mu.readthedocs.io/en/latest/
Which links to github (Watch button):
https://github.com/mu-editor/mu/
I guess they didn't want "users" to accidentally think they need GitHub or read the "developer docs".