[capi-sig] How to assign docstring for built-in methods?

Hi, I am trying to figure out if I can pass a custom docstring for builtin methods like tp_init of my C extension class. I tried method tables, but that does not work for these special methods. Python puts some documentation automatically which I want to override with the correct parameter descriptions etc:

__init__(...) x.__init__(...) initializes x; see help(type(x)) for signature

I tried asking this in more generic forums, but got no authoritative answer.

Thanks, Subha