Add issue-template label guidance

[lpc0387]

7. Add issue-template label guidance

Labels: good first issue, documentation, github

Body:

The repository has GitHub issue templates for bug reports, docs, and feature requests. Add a short maintainer-facing note that suggests labels for first-response triage, including good first issue, documentation, tests, dashboard, and sandbox.

Suggested scope:

• Update CONTRIBUTING.md, a launch doc, or the issue template descriptions with lightweight label guidance.
• Keep guidance advisory; do not require a specific GitHub label configuration file.
• Mention that security vulnerabilities should still follow SECURITY.md instead of public issues.
• Do not create labels or issues through the GitHub API.

Acceptance criteria:

• Maintainers have a concise reference for which labels fit common newcomer-friendly issues.
• The note preserves the existing security-reporting boundary.
• The guidance does not depend on labels already existing in the remote repository.
• Verification notes include Markdown review only.

Why it is newcomer-friendly:

This is a low-risk repository hygiene task that helps future contributors and maintainers without requiring code changes.

---

This issue was created from the v5.0 launch backlog in docs/launch/good-first-issues.md.

[chenlinxi890-spec]

I checked the issue body and the existing issue templates. The guidance suggests adding label suggestions to CONTRIBUTING.md or the issue template descriptions. I can add a concise label guidance section to CONTRIBUTING.md mentioning good first issue, documentation, tests, dashboard, sandbox labels. Would you accept a minimal PR for this?

[lpc0387]

I checked the issue body and the existing issue templates. The guidance suggests adding label suggestions to CONTRIBUTING.md or the issue template descriptions. I can add a concise label guidance section to CONTRIBUTING.md mentioning good first issue, documentation, tests, dashboard, sandbox labels. Would you accept a minimal PR for this?

Of course, thank you for your contribution. @chenlinxi890-spec