fix(graphql-model-transformer): callout extend type support limitation

Author: sundersc

src/pages/gen1/[platform]/build-a-backend/graphqlapi/data-modeling/index.mdx

@@ -1142,6 +1142,9 @@ Declaring custom Query, Mutation, and/or Subscription with the same field names
 `🛑 Object type extension 'Query' cannot redeclare field getBlogById`
 </Callout>
 
+<Callout info>
+The 'extend' keyword can only be applied to GraphQL Queries, Mutations, and Subscriptions. Amplify directives are not supported on these extended type definitions.
+</Callout>
 
 ## How it works