[DOCS] Add Modin and sklearn example with discussion #2417
Description
Link to example in the repo: https://github.com/modin-project/modin/blob/master/examples/modin-scikit-learn-example.ipynb
Related to #2414
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Link to example in the repo: https://github.com/modin-project/modin/blob/master/examples/modin-scikit-learn-example.ipynb
Related to #2414