Update video-series-overview.md

[alysethurber]

Description

Fixed goals box to be consistent with other note, made all tutorial headers consistent in size, and removed dead link to 'Get started with QGreenland'

Checklist

If an item on this list is done or not needed, check it with [x] or click the checkbox.

• [x] The PR description links to issues that it resolves with closes #{issue_number}
• [x] Config lockfile updated (inv config.export > qgreenland/config/cfg-lock.json)
• [x] Environment lockfile updated if needed (conda-lock)
• [x] Version bumped if needed (bumpversion (major|minor|patch|prerelease|build))
• [x] CHANGELOG.md updated
• [x] Documentation updated if needed
• [x] New unit tests if needed

[trey-stafford]

Thanks, @alysethurber! I'll take a look at these changes later. FWIW, I have a PR that updates a lot of the documentation in the works right now. You can take a look here: https://github.com/nsidc/qgreenland/pull/711