Docs issue template should ask reporters to search existing issues first

What is the issue?

The documentation issue template does not currently remind reporters to search existing issues before opening a new docs report.

That guidance exists in the bug report and feature request templates, and it also matches docs/contributing.md, which asks external contributors to open or upvote existing issues/discussions rather than opening unsolicited code PRs.

Adding a short reminder to .github/ISSUE_TEMPLATE/6-docs-issue.yml would make docs reports consistent with the other issue templates and could reduce duplicate documentation issues.

I searched for related existing issues with queries around docs issue template, Documentation Issue, and search existing issues, and did not find an exact match.

Where did you find it?

• https://github.com/openai/codex/blob/main/.github/ISSUE_TEMPLATE/6-docs-issue.yml
• https://github.com/openai/codex/blob/main/.github/ISSUE_TEMPLATE/4-bug-report.yml
• https://github.com/openai/codex/blob/main/.github/ISSUE_TEMPLATE/5-feature-request.yml
• https://github.com/openai/codex/blob/main/docs/contributing.md