docs: shopping list clarification

bindings/README.md

@@ -40,6 +40,7 @@ This library exports methods:
     // combines ingredient lists into one
     // usage example:
     // let all_recipe_ingredients_combined = combine_ingredients(recipe.ingredients);
+    // if multiple recipes need to be combined, combine their ingredients lists and pass them to this method
     combine_ingredients(ingredients: Vec<Ingredient>) -> IngredientList;
     // combines ingredient lists into one
     // usage example:

bindings/src/model.rs

@@ -411,6 +411,7 @@ pub(crate) fn into_simple_recipe(recipe: &OriginalRecipe) -> CooklangRecipe {
     }
 
     // Process metadata
+    // TODO: add support for nested metadata
     for (key, value) in &recipe.metadata.map {
         if let (Some(key), Some(value)) = (key.as_str(), value.as_str()) {
             metadata.insert(key.to_string(), value.to_string());