PR template todos
Introduced tick box in PR template that new `TODO`s link to an issue.
@@ -21,6 +21,7 @@ the terms of the Apache 2.0 license.
- [ ] API changes follow the [Runbook for Firecracker API changes][2].
- [ ] User-facing changes are mentioned in `CHANGELOG.md`.
- [ ] All added/changed functionality is tested.
+- [ ] New `TODO`s link to an issue.
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