Add a function that reads named_features.csv into a pandas DataFrame

The pandas package excels at storing and manipulating tabular data. The file `/data/named_features.csv` is a table of named features on Pluto and some facts about them.

Write a function in helpers.py that:

- reads the named_features.csv into a pandas dataframe

Add an example in `jupyter_notebooks/` (you can edit `tutorial.ipynb` or make your own notebook) which shows how to call this function and some cool manipulations you can do with pandas methods.