Inconsistent inherited docstrings

A few estimators subclass estimators from other ML packages (e.g. scikit-learn) and when a method is not overwritten, the docstring from the parent package is used directly in the documentation, which is not necessarily consistent. For instance,
* docstrings inherited from scikit-learn where [the variable dtype includes sparse arrays](http://dask-ml.readthedocs.io/en/latest/search.html?q=sparse&check_keywords=yes&area=default)
* ["see also" sections](http://dask-ml.readthedocs.io/en/latest/modules/generated/dask_ml.linear_model.PartialPerceptron.html?highlight=sparse) that points to scikit-learn estimators etc.

I wonder if some automatic re-writing of the non-overwritten methods could partially address this...