DOC: Add pandas video series to tutorials.rst
This is a 6-hour video tutorial series that is freely available on YouTube. If you would like to quickly preview the contents of the series, you can see all of the code in this [Jupyter Notebook](http://nbviewer.jupyter.org/github/justmarkham/pandas-videos/blob/master/pandas.ipynb).

Collectively, these videos have nearly 20,000 likes across 1 million views. If you would like to read some testimonials about the quality of the instruction, [please see here](https://www.dataschool.io/testimonials/#aboutmypandasvideoshttpwwwdataschoolioeasierdataanalysiswithpandas).

Please let me know if you have any questions or would like me to make any changes. Thanks for your consideration!