add easy way to access 'Datasets used in ISLP'

[behrica]

https://intro-stat-learning.github.io/ISLP/data.html python client: https://github.com/uci-ml-repo/ucimlrepo/blob/main/src/ucimlrepo/fetch.py

This page seems to say that all dataset have creative-common licence: https://archive.ics.uci.edu/contribute/donation

Some / few / most datasets only have "metadata" it seems, to be verified.