Merge branch 'master' into python-string-formatting-update

Author: lpozo

pivot_tables/README.md

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+These are the three download files you can use with the Real Python tutorial [How to Create a Pivot Table With pandas](https://realpython.com/how-to-pandas-pivot-table/):
+
+code_downloads.ipynb contains the main code from the tutorial.
+solutions.ipynb contains sample solutions to the various exercises.
+sales_data.csv contains the source data used throughout the tutorial.