[Bug] Runbook for API changes link in PR template is broken

[georgepisaltu]

Describe the bug

The link to the Runbook for API changes in our Pull Request template is broken (displayed as https://github.com/firecracker-microvm/firecracker/docs/api-change-runbook.md).

Expected behaviour

Link should point to a valid version of the document.

Additional context

In this comment on the runbook PR we established that we want a relative link to the runbook in our PR template so that it would be valid across branches.

When visiting the document in GitHub, link here, the link works correctly. However, when looking at a PR, the link is broken. I think this has to do with the way GitHub generates the PR from the template and the quickest solution would be to have a permanent link to the latest version of the file on the main branch.

Checks

• [ ] Have you searched the Firecracker Issues database for similar problems?
• [ ] Have you read the existing relevant Firecracker documentation?
• [ ] Are you certain the bug being reported is a Firecracker issue?