Add documentation for DocumentBar

[nateinaction]

What?

Part of: #60358

Added JSDoc to DocumentBar component and rendered documentation for the readme.

How?

Added JSDocs formatted doc blocks to existing DocumentBar component.
Ran npm run docs:build to render new README.md

[github-actions]

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Co-authored-by: nateinaction <[email protected]>
Co-authored-by: colorful-tones <[email protected]>

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[github-actions]

👋 Thanks for your first Pull Request and for helping build the future of Gutenberg and WordPress, @nateinaction! In case you missed it, we'd love to have you join us in our Slack community.

If you want to learn more about WordPress development in general, check out the Core Handbook full of helpful information.

[ntsekouras]

LGTM, thanks!