Add dataset statistics in the documentation

[abonte]

Hi all,

I'm wondering if it would be useful to add some statistics of each dataset in the documentation like the number of classes, samples per class, samples total, dimensionality and feature types.
E.g., https://scikit-learn.org/stable/modules/generated/sklearn.datasets.load_iris.html#sklearn.datasets.load_iris

In case of positive feedback, I will open an issue.

Thanks