DOC dataset doc add return and improve doc #3315

Fixes #3315 
What do you think @arjoly ?
IMO, it's good....


On 26 June 2014 19:27, Ilambharathi Kanniah <notifications@github.com>
wrote:

>  In sklearn/datasets/california_housing.py:
>
> > @@ -56,6 +60,22 @@ def fetch_california_housing(data_home=None, download_if_missing=True):
> >          If False, raise a IOError if the data is not locally available
> >          instead of trying to download the data from the source site.
> >
> > +    Returns
> > +    -------
> > +    The data is returned as a Bunch object with the following attributes:
>
> Yes, that would be right too.
>
> bunch : Bunch object with the attributes as follows
> bunch.data : sparse matrix, shape [n_samples, n_features] - What data has description
> bunch.target : array, shape [n_samples] - What target has description
> bunch.target_names : list, length [n_classes] - What target_names has description
>
> Would this be a good format ? Because it would be good to have the
> description of each of the attributes as well.
>
> —
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> <https://github.com/scikit-learn/scikit-learn/pull/3316/files#r14272966>.
>