Add a documentation blurb to the new issue template to encourage writing (better) documentation.

.gitlab/issue_templates/Feature Proposal.md

@@ -5,3 +5,13 @@
 ### Proposal
 
 ### Links / references
+
+### Documentation blurb
+
+(Write the start of the documentation of this feature here, include:
+
+1. Why should someone use it; what's the underlying problem.
+2. What is the solution.
+3. How does someone use this
+
+During implementation, this can then be copied and used as a starter for the documentation.)