docs: update supplemental root README.md (#6123)

* docs: update supplemental root README.md

* docs: fix paths

Author: kuhe

supplemental-docs/README.md

@@ -9,3 +9,11 @@ Information about initializing an SDK client and common configurable constructor
 #### [Upgrading](../UPGRADING.md)
 
 Upgrading from AWS SDK for JavaScript (v2) (https://github.com/aws/aws-sdk-js).
+
+#### [AWS Lambda](./AWS_LAMBDA.md)
+
+Best practices for working within AWS Lambda using the AWS SDK for JavaScript (v3).
+
+#### [TypeScript](./TYPESCRIPT.md)
+
+TypeScript tips & FAQ related to this project.