.gitlab: Update feature template

From https://gimp.org/bugs/report.html:

> Related to bug reports are enhancement requests. It is recommended to discuss enhancements with developers first, for instance on IRC or in the forums. This is to make sure that the enhancement requests that are filed are well-specified and aligned with the overall goals the developers have for GIMP.

.gitlab/issue_templates/feature.md

@@ -1,17 +1,24 @@
 <!-- ⚠️ IMPORTANT: READ ME! ⚠️
-This is the template for feature requests.
-For bug reports, performance issues and security reports, please switch instead to the appropriate template in the "Choose a template" list.
+This is the template for TECHNICAL FEATURE REQUESTS.
+For bug reports, performance issues and security reports, please see:
+https://testing.gimp.org/bugs/report.html#select-the-issue-template
 
 It is important that you fill all the fields of the template. -->
 
 ### Description of the feature
 
 <!-- Please describe your feature with details. Also:
-- If the feature is UI-related, please DO NOT REPORT HERE but on
-  gimp-ux: https://gitlab.gnome.org/Teams/GIMP/Design/gimp-ux/-/issues;
+
+- If the feature is UI-related, please DO NOT REPORT HERE. First,
+  you should discuss with the community and developers in the forums or
+  talk with the developers on IRC: https://www.gimp.org/discuss.html. Then,
+  if it really seems to align with GIMP, report it on gimp-ux:
+  https://gitlab.gnome.org/Teams/GIMP/Design/gimp-ux/-/issues;
+
 - If the feature is about some image file format on GIMP, first check if it
   is not already listed on https://developer.gimp.org/core/coding/standards/images,
   then you can make the request, ideally linking relevant resources (e.g. specs);
+
 - If you have a patch, see: https://developer.gimp.org/core/submit-patch/ -->
 
 ### Use cases