Contributions guidelines

Author: thomasleplus

.github/pull_request_template.md

@@ -0,0 +1,12 @@
+<!-- prettier-ignore-start -->
+<!-- markdownlint-disable-next-line MD041 -->
+## Readiness checklist
+<!-- prettier-ignore-end -->
+
+Please check the boxes below to confirm that you have followed the
+required guidelines for contributions:
+
+- [ ] If this pull request includes code changes, they were all properly tested. Automated tests where also included where possible.
+- [ ] This pull request includes the relevant documentation for this change (if applicable).
+- [ ] All the commits in this pull request where squashed into a single commit. That commit is [signed](https://docs.github.com/en/authentication/managing-commit-signature-verification).
+- [ ] If this pull request is about and existing issue, I added the `Fix #ISSUE_NUMBER` or `Close #ISSUE_NUMBER` text to the description of the pull request.

CONTRIBUTING.md

@@ -16,6 +16,9 @@ request. We then kindly ask that:
 - before working or submitting a large pull request, please open an
   issue to discuss what you have in mind and check that there is not
   an existing solution or a different approach.
+- all code changes must be tested manually and automated tests should
+  be included when possible.
+- all necessary documentation should be included as well.
 - commits on a single pull request must be squashed together to keep
   make reviews easier.
 - commits must be signed (this is supported by most Git clients as