issues: features are better discussed before filing

.gitlab/issue_templates/Feature.md

@@ -1,7 +1,10 @@
 <!-- Please note that some features missing in the stable release are already available in the
 development version. To avoid duplicates and unnecessary issues, please check that your request is
 for something that is not yet implemented, and doesn’t have an existing issue that is open or that
-was closed as out of scope. -->
+was closed as out of scope.
+We also recommend talking to us in the #fractal:gnome.org Matrix room first. We do not intend to
+implement everything and don’t want our issue tracker to become a giant wishlist, but rather a
+curated list of known problems and planned features. -->
 
 Detailed description of the feature. Provide as much information as you can.