docs: begin adding per-audit docs

[woodruffw]

• [x] artipacked
• [x] dangerous-triggers
• [x] excessive-permissions
• [x] hardcoded-container-credentials
• [x] impostor-commit
• [x] known-vulnerable-actions
• [x] ref-confusion
• [x] self-hosted-runner
• [x] template-injection
• [x] use-trusted-publishing