Update Readme for newer library version

[mit-aws]

Issue:

• Current code sample is not working as expected.
• The SNS topic is not able to publish a message without valid policy which gives permission to SNS topic to send message to subscribed SQS queue.

Description of changes:

Code Sample

• Attach the policy to SQS queue to receive messages from subscribed SNS topic.
• Update the SQS client's recieve_message attributes to receive consistent output.
• Delete the received_messages from SQS queue
• Add the case to publish a message through PlatformEndpoint Resource.

Required changes for the migration from s3 resource interface to client

• Updates the description of s3_client attribute of sns_extended_client
• Updates the example to set custom s3 config for s3_client attribute

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[jagdev-aws]

LGTM

[jagdev-aws]

Looks good to me