prefs: Note that favourite confirmation applies to Glitch flavour only (#491)

config/locales/simple_form.en.yml

@@ -55,7 +55,7 @@ en:
         setting_default_sensitive: Always mark media as sensitive
         setting_delete_modal: Show confirmation dialog before deleting a toot
         setting_display_sensitive_media: Always show media marked as sensitive
-        setting_favourite_modal: Show confirmation dialog before favouriting
+        setting_favourite_modal: Show confirmation dialog before favouriting (applies to Glitch flavour only)
         setting_hide_network: Hide your network
         setting_noindex: Opt-out of search engine indexing
         setting_reduce_motion: Reduce motion in animations