doc(data): support for serial identifiers

Author: p5quared

src/pages/[platform]/build-a-backend/data/data-modeling/identifiers/index.mdx

@@ -66,8 +66,8 @@ print("New Todo created: \(createdTodo)")
 </InlineFilter>
 
 If you want, you can use Amplify Data to define single-field and composite identifiers:
-- Single-field identifier with a consumer-provided value (type: `id` or `string`, and must be marked `required`)
-- Composite identifier with a set of consumer-provided values (type: `id` or `string`, and must be marked `required`)
+- Single-field identifier with a consumer-provided value (type: `id` or `string` marked `required`, or for a [serial identifier](/[platform]/build-a-backend/data/data-modeling/add-fields/#assign-default-values-for-fields), type: `integer` marked `default`)
+- Composite identifier with a set of consumer-provided values (type: `id` or `string` marked `required`, or for a [serial identifier](/[platform]/build-a-backend/data/data-modeling/add-fields/#assign-default-values-for-fields), type: `integer` marked `default`)
 
 ## Single-field identifier