set CDK_DEFAULT_REGION env variable with aws configure command

Author: ksmin23

README.md

@@ -97,7 +97,7 @@ At this point you can now synthesize the CloudFormation template for this code.
 
 <pre>
 (.venv) $ export CDK_DEFAULT_ACCOUNT=$(aws sts get-caller-identity --query Account --output text)
-(.venv) $ export CDK_DEFAULT_REGION=$(curl -s 169.254.169.254/latest/dynamic/instance-identity/document | jq -r .region)
+(.venv) $ export CDK_DEFAULT_REGION=$(aws configure get region)
 (.venv) $ cdk synth --all
 </pre>