Add datascience notebooks to docs

[raybellwaves]

Copy from https://github.com/raybellwaves/xskillscore-tutorial

Add another example on how it can be used in lieu of pandas.groupby.apply

[bradyrx]

See the badge here (under tutorials): https://climpred.readthedocs.io/en/latest/. We can add a custom badge with a direct link.

[raybellwaves]

See the badge here (under tutorials): climpred.readthedocs.io/en/latest. We can add a custom badge with a direct link.

Nice. I'm +1 for that. I'll may still add a slightly different version to the docs

[raybellwaves]

TODO:

• [] Does this bring benefit than just using scikit-learn, pandas and numpy for evaluating forecasts of tabular data (i.e. may be handling big data?)
• [] Can the Contingency metrics be added as accessors to supplement scikit-learn classification metrics.

[raybellwaves]

raybellwaves/xskillscore-tutorial#3

[raybellwaves]

Closed via https://xskillscore.readthedocs.io/en/stable/tabular-data.html