feat: add gomarklint to Tools section

[shinagawa-web]

What

Add gomarklint to the Tools section.

Why

gomarklint is a Markdown linter that fits well into Hugo content workflows:

• Single binary, no Node.js or Ruby required — easy to add to Hugo CI pipelines
• Built-in HTTP link validation — catches broken external links in content before deploy
• 100,000+ lines in ~170ms — fast enough for large Hugo content repositories
• GitHub Actions integration: https://github.com/shinagawa-web/gomarklint-action
• pre-commit support included (.pre-commit-hooks.yaml)

Links

• Repo: https://github.com/shinagawa-web/gomarklint
• Docs: https://shinagawa-web.github.io/gomarklint/
• Latest release: v2.8.0