Update README.md to recommend upgrading SDK for security patches.
Update README.md to recommend upgrading SDK for security patches.


cedral/aws-sdk-cpp,awslabs/aws-sdk-cpp,awslabs/aws-sdk-cpp,aws/aws-sdk-cpp,cedral/aws-sdk-cpp,aws/aws-sdk-cpp,cedral/aws-sdk-cpp,aws/aws-sdk-cpp,aws/aws-sdk-cpp,cedral/aws-sdk-cpp,awslabs/aws-sdk-cpp,cedral/aws-sdk-cpp,aws/aws-sdk-cpp,aws/aws-sdk-cpp,awslabs/aws-sdk-cpp,cedral/aws-sdk-cpp