doc: Point pull request template to contributors guide (#549)

.github/PULL_REQUEST_TEMPLATE.md

@@ -13,6 +13,9 @@ Helpful information to understand the project can be found here: [CONTRIBUTING](
 # Checklist
 Please put a X in the boxes as evidence of reading through the checklist.
 
+- [ ] I have read the [CONTRIBUTORS](CONTRIBUTORS.adoc) guide
+  - [ ] I considered the "3 line" suggestion.
+  - [ ] I followed the "1 logical change" rule.
 - [ ] I have forked the project, and raised this PR on a feature branch.
 - [ ] I ran the `pre-commit` hooks, and my commit message was validated.
 - [ ] `make -wC service compile` runs without any issues.

CONTRIBUTING.adoc

@@ -11,11 +11,11 @@ Ideas may be discussed, purely on their merits and issues. Our Code of Conduct
 discussion throughout the whole process. This project respects the
 link:https://www.kernel.org/doc/html/latest/process/code-of-conduct.html[Linux Kernel code of conduct].
 
-== More than 3 lines - talk to someone first
+== Suggestion: More than 3 lines - talk to someone first
 
-If you're planning on making a change that's more than a 3 lines, please talk to someone first. This is so that you don't waste your time on something that might not be accepted. It's also a good way to get some feedback on your idea and make sure you're on the right track.
+If you're planning on making a change that's more than a 3 lines, please talk to someone first (raising a GitHub issue is the best way to do that). This is so that you don't waste your time on something that might not be accepted. It's also a good way to get some feedback on your idea and make sure you're on the right track.
 
-== A PR should be one logical change
+== Rule: A PR should be one logical change
 
 Please try to keep your pull requests small and focused. It's almost impossible to review PRs that change lots of files for lots of different reasons. If you have a big change, it's probably best to break it down into smaller, more manageable chunks, otherwise it's likely to be rejected.
 
@@ -30,7 +30,7 @@ the general direction and roadmap of this project without asking.
 
 The preferred way to communicate is probably via Discord or GitHub issues.
 
-=== Dev environment setup and clean build
+== Dev environment setup and clean build
 
 ```
 # Step1: setup compile env