update citation docs

[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.

Related Tickets & Documents

Closes #665

PR Checklist

General

• PR includes a summary of changes
• Link relevant issues, make one if none exist
• Add a brief summary of changes to docs/release-notes.rst in a relevant section for the upcoming release.
• Add appropriate labels to this PR
• PR follows the Contributor's Guide

[anissa111]

I think linking to the zenodo page is a way better practice than maintaining a separate citations page, anyway.

Thank you for doing this!

[jukent]

Great idea. I wonder if there are other broken links in our documentation that we need to look for now.

[kafitzgerald]

Great idea. I wonder if there are other broken links in our documentation that we need to look for now.

I presumed these would also have be caught by the link checker, but in doing a quick search of the code found a link to out to the roadmap as well that we missed. I'll go ahead and wrap that in here as well.