[FEATURE] Add AGENTS.md for users, contributors and maintainers using agentic AI

[pylapp]

Is your feature request related to a problem?

Some contributors can feel a bit lost with the ail of the project and its structure.
GenAI is used more and more, and an AGENTS.md can help people using, contributing and maintaing the project.

What solution would you like?

An AGENTS.md file like this one for example.

What alternatives have you considered?

None

Do you have any additional context?

No