Adapt issue/PR template to better reflect contribution policy

Author: peterthomassen

.github/ISSUE_TEMPLATE/1-issue.md

@@ -5,6 +5,13 @@ about: Please only raise an issue if you've been advised to do so after discussi
 
 ## Checklist
 
+<!--
+Note: REST framework is considered feature-complete. New functionality should be implemented outside the core REST framework. For details, please check the docs: https://www.django-rest-framework.org/community/third-party-packages/#about-third-party-packages
+-->
+
 - [ ] Raised initially as discussion #...
-- [ ] This cannot be dealt with as a third party library. (We prefer new functionality to be [in the form of third party libraries](https://www.django-rest-framework.org/community/third-party-packages/#about-third-party-packages) where possible.)
+- [ ] This is not a feature request suitable for implementation outside this project. Please elaborate what it is:
+  - [ ] compatibility fix for new Django/Python version ...
+  - [ ] other type of bug fix
+  - [ ] other type of improvement that does not touch existing code or change existing behavior (e.g. wrapper for new Django field)
 - [ ] I have reduced the issue to the simplest possible case.

PULL_REQUEST_TEMPLATE.md

@@ -1,4 +1,4 @@
-*Note*: Before submitting this pull request, please review our [contributing guidelines](https://www.django-rest-framework.org/community/contributing/#pull-requests).
+*Note*: Before submitting a code change, please review our [contributing guidelines](https://www.django-rest-framework.org/community/contributing/#pull-requests).
 
 ## Description