add skewt plot

[jukent]

PR Summary

First pass at demonstrating get_skewt_vars
Related to #126

PR Checklist

General

• Make an issue if one doesn't already exist
• Link the issue this PR resolves by adding closes #XXX to the PR description where XXX is the number of the issue.
• Add a brief summary of changes to docs/release-notes.rst in a relevant section for the next unreleased release. Possible sections include: Documentation, New Features, Bug Fixes, Internal Changes, Breaking Changes/Deprecated
• Add appropriate labels to this PR
• Make your changes in a forked repository rather than directly in this repo
• Open this PR as a draft if it is not ready for review
• Convert this PR from a draft to a full PR before requesting reviewers
• Passes precommit. To set up on your local, run pre-commit install from the top level of the repository. To manually run pre-commits, use pre-commit run --all-files and re-add any changed files before committing again and pushing.
• [ ]
  Examples
• Any new notebook examples added to docs/examples/ folder
• Clear all notebook cells
• New notebook files added to docs/examples.rst toctree
• New notebook files added to new entry in docs/gallery.yml with appropriate thumbnail photo in docs/_static/thumbnails/

[kafitzgerald]

This looks great!

It looks like there's a merge conflict though.

Should we add this to the release notes as well? I think we might have missed your other usage example as well in there.