documentation structure setup

[HaleySchuhl]

Describe your changes
Basic documentation structure setup and a few standard doc pages adapted from PlantCV main package and plantcv.annotate.

Type of update
Is this a:

• Update to documentation
• Work in progress

Associated issues
Reference associated issue numbers. Does this pull request close any issues?

Additional context
Add any other context about the problem here.

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 932d28f..908cb5d. 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	100%	100%
Line Coverage	100%	100%

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I reviewed it myself