add doc for deep diff

src/models/recipe.rs

@@ -208,6 +208,8 @@ impl Recipe {
         menu1 == menu2
     }
 
+    /// Similar to `diff_pd_between_recipes` but will check each field of
+    /// recipe and list them out if any.
     pub fn deep_diff_pd_between_recipes(
         &self,
         another_recipe: &Recipe,