Add MR template with basic instructions
Following essentially unnecessary Slack requests to approve recent, small MRs, we removed the Prevent approval by author
requirement for good.
This MR template clarifies which MRs here actually need a review (which mostly means a test) and which don't.
Context
See #2 & !19 (merged) for context about why we initally set up that requirement.
Edited by Katrin Leinweber