add instructor notes (tidy data)

[chennesy]

How could the content be improved?

Outline option for instructors to teach the tidy-data episode only as a conceptual lesson and skip the live coding using df.melt() and the datetime conversion, since these can be difficult concepts to grasp for beginners. Instructors can skip to the data-viz episode in that case and import the df_long.pkl from the data.zip download at the beginning of the episode to work with the updated dataset.

Note: transferred manually from chennesy repo fork since Issue transfer wasn't available to this repo.

Which part of the content does your suggestion apply to?

https://librarycarpentry.org/lc-python-intro/instructor/tidy.html