chore: Add guidance with links to use Amplify over AppSync SDK (#544)

Author: kevinold

README.md

@@ -1,3 +1,10 @@
+## Recommendation: Use [Amplify](https://aws-amplify.github.io/) clients to connect to AppSync
+
+For front-end web and mobile development, we recommend using the [Amplify](https://aws-amplify.github.io/) clients which are optimized to connect to the AppSync backend.
+
+- For DynamoDB data sources, use the [DataStore](https://docs.amplify.aws/lib/datastore/getting-started/q/platform/ios/) category in the Amplify client. It provides the best developer experience and built-in conflict detection and resolution.
+- For non-DynamoDB data sources in scenarios where you have no offline requirements, use the [API (GraphQL)](https://docs.amplify.aws/lib/graphqlapi/getting-started/q/platform/ios/) category in the Amplify client.
+
 AWS AppSync SDK for iOS
 =======================