docs: mention Playground and downstream users organized by usage level

[Copilot]

The docs did not previously highlight known downstream adopters or a clear reference implementation, which made onboarding harder.

Changes

• docs/index.md: added a Who uses this? section organized by usage level:

  • Playground (featured): elastic/ai-github-actions-playground as the reference implementation running the full workflow suite
  • Heavy users: elastic/beats, elastic/integrations
  • Light users: strawgate/py-key-value

• README.md: added a compact Who uses this? summary with the same tiers and a link to the full docs section.

• Fixes Mention the Playground in docs #361

Generated by Update PR Body

[coderabbitai]

📝 Walkthrough

Walkthrough

Documentation updates to README.md and docs/index.md that introduce a new "Who uses this?" section, showcasing usage examples including the Playground and notable user projects across different deployment scales.

Changes

Cohort / File(s)	Summary
Documentation: Who Uses This Section README.md, docs/index.md	Added "Who uses this?" subsections with playground link and examples of heavy users (elastic/beats, elastic/integrations) and light users (strawgate/py-key-value). Content-only additions with no logic or functionality changes.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 Documentation hops along the trail,
New examples tell our story well,
From playgrounds to integrations bright,
Who uses this? The docs shine light! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main documentation changes: adding playground and downstream users organized by usage level, matching the PR's core objective.
Linked Issues check	✅ Passed	The PR fully addresses all coding requirements from issue #361: documenting the playground as a reference implementation and surfacing all four specified downstream users organized by usage level.
Out of Scope Changes check	✅ Passed	All changes are documentation-only updates directly addressing the linked issue requirements; no unrelated modifications or scope creep detected.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch copilot/mention-playground-in-docs

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