Update citation docs and remove broken link

[kafitzgerald]

PR Summary

Removes the broken link to the old GeoCAT website citation page and makes a few minor updates to the citation docs for clarity.

The old GeoCAT website citation page for reference: https://github.com/NCAR/GeoCAT/blob/gh-pages/pages/citation.md

At some point we might consider removing the examples on here and swapping them for a sample BibTex entry which is a bit more generic (i.e. not specific to a particular citation style) as well.

Closes #258

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.

[kafitzgerald]

Just noting the failures here are not from the changes but rather a pre-existing issue addressed by #257, which should probably just be merged first. Adding a blocked label to make that more obvious.

[jukent]

Just noting the failures here are not from the changes but rather a pre-existing issue addressed by #257, which should probably just be merged first. Adding a blocked label to make that more obvious.

Was going to ask why this was blocked. Don't you love when 2 PRS are failing because the other isn't merged yet?