Added a new resource

[sandeepmishratech]

Hey, I have added a new resource in the reference for Python Classes. I found this tutorial online while looking for some resources to learn python. Topics were explained pretty well and found it to be useful and thought of adding it here. Hope this small contribution will help other learners.

[ethen8181]

Hi @sandeepmishratech , thanks for sharing it. FYI, we don't actually edit the html ourselves, we modify the jupyter notebook version of the documentation, https://github.com/ethen8181/machine-learning/blob/master/python/class.ipynb, then html files are generated via the [convert_to_html.py](https://github.com/ethen8181/machine-learning/blob/master/convert_to_html.py) script