Add non-CLI documentation for Naive Bayes

[HaleySchuhl]

Is your feature request related to a problem? Please describe.
Not all users feel comfortable using the terminal, and we have found that reducing the number of times a user needs to switch applications can enhance the experience. It would be beneficial to add jupyter notebook/straight python documentation on ReadTheDocs and in the tutorial for Naive Bayes.

Describe the solution you'd like

from plantcv import learn

learn.naive_bayes_multiclass(pixelinspectdata.txt, naive_bayes_pdfs.txt)

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context

• request initiated by Syntax Error when trying to run plantcv-train #1590