Update project thread update docs

[zackkrida]

Fixes

Fixes #2249 by @zackkrida

Description

Updates project thread update documentation, removes the template, and links to some real-world examples from the repo. Oh, and also fixes some unrelated typos.

Testing Instructions

Let me know if you think this is sufficient information for project leads and contributors on how to leave updates. Keep in mind that folks will be directed to this section from the automated reminders in #2251, which state:

Hi @${recipient}, this project has not received an update comment in 14 days. Please leave an update comment as soon as you can. See the documentation on project updates for more information.

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (if applicable).

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[github-actions]

Full-stack documentation: https://docs.openverse.org/_preview/2329

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[AetherUnbound]

This looks great, and I appreciate the links to existing examples too!

[sarayourfriend]

I've left some small editorial suggestions but otherwise this LGTM and captures the result of the discussion well.