Add DevRel request item to PR checklist (#5783)

Co-authored-by: Joshua Batty <joshpbatty@gmail.com>

Author: IGI-111

.github/PULL_REQUEST_TEMPLATE.md

@@ -6,6 +6,7 @@
 - [ ] I have linked to any relevant issues.
 - [ ] I have commented my code, particularly in hard-to-understand areas.
 - [ ] I have updated the documentation where relevant (API docs, the reference, and the Sway book).
+   - [ ] If my change requires substantial documentation changes, I have [requested support from the DevRel team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
 - [ ] I have added tests that prove my fix is effective or that my feature works.
 - [ ] I have added (or requested a maintainer to add) the necessary `Breaking*` or `New Feature` labels where relevant.
 - [ ] I have done my best to ensure that my PR adheres to [the Fuel Labs Code Review Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).