Update CONTRIBUTRING.md to reduce unnecesarry review workload

Author: jonasschnelli

CONTRIBUTING.md

@@ -157,6 +157,14 @@ behaviour of code within the pull request (bugs must be preserved as is).
 Project maintainers aim for a quick turnaround on refactoring pull requests, so
 where possible keep them short, uncomplex and easy to verify.
 
+Pull requests that refactor the code should not be made by new contributors. It
+requires a certain level of experience to know where the code belongs to and to
+understand the full ramification (including rebase effort of open pull requests).
+
+Trivial pull requests or pull requests that refactor the code with no clear
+benefits may be immediately closed by the maintainers to reduce unnecessary
+workload on reviewing.
+
 
 "Decision Making" Process
 -------------------------