docs: improve first PR walkthrough

Goal

Make the first-PR walkthrough explicitly show that a focused documentation change is a real, reviewable open-source contribution when it solves a tracked issue.

Scope

• Edit only docs/community/FIRST_PR_WALKTHROUGH.md.
• In the browser-only docs section, add a short explanation of what makes a docs-only PR meaningful: it links an issue, satisfies acceptance criteria, improves a real user or contributor workflow, and stays focused.
• Add the missing GitHub web-editor steps: preview the Markdown diff, choose a new branch, and include Closes #44 in the PR body.
• Add a small docs-only PR body example that names the change and says Docs review only; checked the GitHub Markdown preview.
• State clearly that no command-line check is required for this issue.
• Do not change application code, generated Pages HTML, screenshots, audio, archives, or other documentation files.

Acceptance Criteria

• A first-time contributor can complete the change in GitHub without a local clone.
• The walkthrough directly answers whether documentation PRs are taken seriously.
• The new guidance distinguishes useful docs work from splitting trivial typo-only changes for metrics.
• The PR changes only docs/community/FIRST_PR_WALKTHROUGH.md and includes Closes #44.

Start Here

Direct edit link: https://github.com/duct-tape2/ai-language-partner/edit/main/docs/community/FIRST_PR_WALKTHROUGH.md

No command-line verification is required. Use GitHub Markdown preview and describe that review in the PR body.