Add link to source code from arabidopsis_multi_plant_tutorial.md

[HaleySchuhl]

add github button to link to source code from the arabidopsis multiplant tutorial documentation page.

Type of update Is this a:

• Bug fix
• Update to documentation

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

[codecov[bot]]

Codecov Report

Merging #1348 (57fa972) into main (d8ae17f) will not change coverage. The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1348   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          156       156           
  Lines         6878      6878           
=========================================
  Hits          6878      6878           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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[nfahlgren]

What if the button code (for three buttons) ultimately looked like this?

[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/danforthcenter/plantcv-tutorial-arabidopsis-tray/HEAD?labpath=index.ipynb)
<a target="_blank" href="https://colab.research.google.com/github/danforthcenter/plantcv-tutorial-arabidopsis-tray">
  <img src="https://colab.research.google.com/assets/colab-badge.svg" alt="Open In Colab"/>
</a>
[![Static Badge](https://img.shields.io/badge/Open%20on%20GitHub-black?style=flat&logo=github)](https://github.com/danforthcenter/plantcv-tutorial-arabidopsis-tray)

[HaleySchuhl]

Looks really nice!

[HaleySchuhl]

Just a draft now, not sure how we want to handle Collab so wait on adding those buttons to docs. Parag is working on this in a new branch