Why does PolyGamma rng_fn get a docstring but not any of the others?

## Description of your problem
As title reads; Why does PolyGamma rng_fn get a docstring but not any of the others?
https://github.com/pymc-devs/pymc/blob/main/pymc/distributions/continuous.py#L3951

Would there be any downside to have docstrings on all the other rng_fn?
