[task] Add a first-PR example to contributing docs

[phongndo]

Area

Docs

Goal

Add a small example PR description for a first-time contributor opening a focused docs change.

Why this matters

The PR template lists what to include, but a concrete example helps students turn a completed issue into a clear reviewable pull request.

Relevant files

• CONTRIBUTING.md
• .github/PULL_REQUEST_TEMPLATE.md only if the example needs to stay aligned with the template

Depends on

None. This can be claimed immediately.

Out of scope

• Do not change the PR template checklist unless a maintainer asks for it.
• Do not add a long tutorial for GitHub pull requests.
• Do not weaken the human-authored PR requirement.

Definition of done

• Contributing docs include a short example PR description for a small docs issue.
• The example includes summary, linked issue, verification commands, and notes for reviewers.
• The example keeps the human-authored PR expectation clear.

Verification

• pnpm format:prettier:check
• Manually review the rendered Markdown or GitHub preview for readability.

Contributor notes

This is a good first issue because it improves contributor guidance without touching product code.

[Za1dKhan]

/claim