Added note to clarify Aws.config purpose.
Added note to clarify Aws.config purpose.

Fixes #1042

takeyuweb/aws-sdk-ruby,aws/aws-sdk-ruby,llooker/aws-sdk-ruby,llooker/aws-sdk-ruby,hamadata/aws-sdk-ruby,aws/aws-sdk-ruby,takeyuweb/aws-sdk-ruby,hamadata/aws-sdk-ruby,cjyclaire/aws-sdk-ruby,llooker/aws-sdk-ruby,takeyuweb/aws-sdk-ruby,aws/aws-sdk-ruby,hamadata/aws-sdk-ruby,cjyclaire/aws-sdk-ruby,cjyclaire/aws-sdk-ruby