Add short quality checklist to pull request template (#2472)

Add short quality checklist to pull request template

.github/PULL_REQUEST_TEMPLATE.md

@@ -10,8 +10,7 @@ Particularly the sections about the:
 
 To help the maintainers out when they're writing release notes, please
 try to include a sentence or two here describing your change for end
-users. See the CHANGELOG.md and CHANGELOG-helmop.md files in the
-top-level directory for examples.
+users. See the CHANGELOG.md file in the top-level directory for examples.
 
 Particularly for ground-breaking changes and new features, it's important to
 make users and developers aware of what's changing and where those changes
@@ -20,4 +19,15 @@ were documented or discussed.
 Even for smaller changes it's useful to see things documented as well, as it
 gives everybody a chance to see at a glance what's coming up in the next
 release. It makes the life of the project maintainer a lot easier as well.
+
+The following short checklist can be used to make sure your PR is of good
+quality, and can be merged easily:
+
+- [ ] if it resolves an issue;
+      is a reference (i.e. #1) to this issue included?
+- [ ] if it introduces a new functionality or configuration flag;
+      did you document this in the references or guides?
+- [ ] optional but much appreciated;
+      do you think many users would profit from a dedicated setting
+      for this functionality in the Helm chart?
 -->