add comment

src/main/kotlin/dev/jsinco/recipes/configuration/RecipesConfig.kt

@@ -209,6 +209,7 @@ class RecipesConfig : AddonConfigFile() {
     class MessagesSection : OkaeriConfig() {
         @CustomKey("already-learned")
         var alreadyLearned = "&rYou already know this recipe!"
+        @Comment("PLACEHOLDERS: %recipe% the name of the recipe.")
         var learned = "&rYou have learned the '&#F7FFC9%recipe%&r' recipe!"
     }
 }