Adds more stories for AnchoredOverlay, BranchName, and Checkbox

[mperrotti]

As I was working on the new primer.style site, I noticed that some of our components were missing helpful Storybook stories.

I also opened a PR to clean up some component docs unrelated to these Storybook changes: primer/design#836

Changelog

No changes that would be shipped.

New

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Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why
  • Only Storybook stories and E2E tests will be updated, so we don't need a release

Testing & Reviewing

Merge checklist

• Added/updated tests
• [N/A] Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

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Latest commit: 5bd9d61

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[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	96.2 KB (0%)
packages/react/dist/browser.umd.js	96.46 KB (0%)

[siddharthkp]

Nice!

[emilybrick]

👍 🌞