Add kmeans tutorial

[k034b363]

Describe your changes
Adding a tutorial for doing kmeans cluster training, classification of a target image, and combining of clusters into binary masks.

Type of update

• Update to documentation

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

Here's the code health analysis summary for commits 7091afc..68b201a. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Python	✅ Success		View Check ↗
Test coverage	✅ Success		View Check ↗

Code Coverage Report

Metric	Aggregate	Python
Branch Coverage	100%	100%
Composite Coverage	99.7%	99.7%
Line Coverage	99.7%	99.7%

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[annacasto]

Looks good! There was just one spot in cell 8 (I think) where it seems like the comment was unfinished:

# Then, once you have picked the clusters belonging to each category, give mask_kmeans a list:
# Remember, the

[k034b363]

Good catch, thank you! I fixed that comment.