It doesn't need to be written by a human only, but I think generating it once and distributing it with source code is more efficient. Developers can correct errors in the generated documentation, which then can be used by humans and LLMs.

Docs are a form of error correcting coding for code. Docs+code allows you to spot discrepancies and ask which one is the intended behavior.

I can read code without the help of LLMs, too. Human documentation tells me why the code was written.