docs(readme): make first-contribution opportunities easy to find #854

Problem

The repository already has a detailed Contributing Guide and has used good first issue / help wanted labels, but its main README.md does not link to the guide or expose a way for new contributors to find approachable issues. Historical starter issues such as #589 and #597 are closed, so the entry point is not currently discoverable.

Scope

Add a short, welcoming Contributing section near the bottom of the English README, using the existing guide instead of repeating setup instructions.

• Link to CONTRIBUTING.md for the existing setup, test, and PR flow.
• Link to the live good first issue and help wanted GitHub label filters:
  • good first issue Good for newcomers
  • help wanted Extra attention is needed
• Explain the distinction in natural language: good first issue is scoped for a first contribution; help wanted welcomes community help but may require more familiarity.
• Invite prospective contributors to comment on the issue before beginning, so ownership and expectations can be clarified.
• Say that contributors can report bugs or propose documentation improvements even when neither filter has open issues.

Acceptance criteria

• The README has a concise, human-readable contributing entry point, with valid relative and GitHub links.
• The guide is not duplicated or rewritten; CONTRIBUTING.md remains the single source of truth.
• No claim that issues are available when the label search is empty; links should remain valid as issues change.
• No code behavior, CI gates, or release automation changes.
• Verify the Markdown links and report any documentation checks actually run.

Contributor notes

This is intentionally a docs-only first contribution. Start with README.md; no Azure subscription is required. Please comment on this issue before taking it. Keep the PR focused on this repository.

Maintainer note

Only label future engineering tasks as good first issue after checking that the change is genuine, unclaimed, bounded, and independently verifiable; do not create artificial work solely to fill the label filter. Keep the existing issue triage, priority, and size conventions.