Docs: Add documentation for overlay button variant

[satya-achanta-venkata]

This change: (check at least one)

• [ ] Adds a new feature
• [ ] Fixes a bug
• [ ] Improves maintainability
• [x] Improves documentation
• [ ] Is a release activity

Is this a breaking change? (check one)

• [ ] Yes
• [x] No

Is the: (complete all)

• [x] Title of this pull request clear, concise, and indicative of the issue number it addresses, if any?
• [ ] Test suite(s) passing?
• [ ] Code coverage maximal?
• [x] Changeset added?
• [ ] Component status page up to date?

What does this change address? This change adds information about overlay button variant. Resolves #382.

Additional context

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 35fc2259b22eb22e07a18d107e31ca0fa9d2c539

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@ithaka/pharos-site	Minor

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[github-actions[bot]]

size-limit report 📦

Path	Size
packages/pharos/lib/index.js	47.05 KB (0%)