Add UI requests note to feature template

The feature request template should not be used for requesting updates to the UI.

There's already a pinned issue for UI customization, and all requests should go there.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -7,6 +7,12 @@ assignees: ''
 
 ---
 
+<!--
+DO NOT REQUEST UI/THEME/GUI/APPEARANCE IMPROVEMENTS HERE
+THESE SHOULD GO IN ISSUE #60
+REQUESTING A NEW FEATURE SHOULD BE STRICTLY RELATED TO NEW FUNCTIONALITY
+-->
+
 **Describe the feature you'd like to see added**
 A short description of the feature, and what it would accomplish.