Link to API Reference Client from README

[trivikr]

Describe the issue with documentation
The client READMEs refer to root README, which provides generic information about v3.
Since API Reference is now available, the client READMEs should refer to API Reference.

Example client-s3 README: https://github.com/aws/aws-sdk-js-v3/blob/master/clients/client-s3/README.md
It currently links to root README https://github.com/aws/aws-sdk-js-v3
It should link to https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/clients/client-s3/classes/s3.html instead. In future, the client README can be populated with examples.

To Reproduce (observed behavior)
Visit landing page for client-s3 API Reference https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/clients/client-s3/index.html

Expected behavior
The README should link to API reference for Client object.

Additional context
Refs: #1877 (comment)

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs and link to relevant comments in this thread.