Add new template for suggestions

.gitlab/issue_templates/Suggestion.md

@@ -0,0 +1,21 @@
+<!--
+Thanks for wanting to submit a suggestion. Please delete
+this text and fill in the template below. If unsure about something, just do as
+best as you're able.
+-->
+
+### Description
+
+[Description of the suggestion]
+
+### Affected UI areas
+
+[For example, the pop-up window or the settings page.]
+
+### Affected core elements
+
+[For example, the clearurls.js or the log.js.]
+
+### Mockup
+
+[Especially ambitious people can add a mockup here.]