Enhance README for the Java section
Enhance README for the Java section

awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples