ecr add docker hub auth code example

Example: push image to ecr

# Get credentials from awscli
aws ecr get-login
# Tag the image with the following filled in.
docker tag e9ae3c220b23 <aws_account_id>.dkr.ecr.<region>.amazonaws.com/<name_in_ecr>
# Push to ECR
docker push <aws_account_id>.dkr.ecr.<region>.amazonaws.com/<name_in_ecr>