Add cdk bootstrap cmd before cdk deploy (#152)

Author: nimicent

README.md

@@ -52,6 +52,10 @@ This exercise code uses [modular AWS SDK for JavaScript][modular-aws-sdk-js] as
 - backend performs create, delete, get, list and update operations on DynamoDB.
 - frontend does put, get, delete operations using an S3 browser client.
 
+- Run: `cdk bootstrap aws://[aws-account-ID]/[region]` 
+- This command:
+  - Creates a CloudFormation stack in the environment.
+
 ### Deploy infrastructure
 
 - Run: `yarn cdk deploy`