Add LocalStack for Snowflake license requirement (#11)

* Add LocalStack for Snowflake license requirement to prerequisites

* Hyperlink LOCALSTACK_AUTH_TOKEN in license prerequisite

* Add auth token guard to start target

Author: HarshCasper

Makefile

@@ -109,6 +109,7 @@ test:			## Run tests
 
 start:			## Start LocalStack
 	@echo "Starting LocalStack..."
+	@test -n "${LOCALSTACK_AUTH_TOKEN}" || (echo "LOCALSTACK_AUTH_TOKEN is not set. Find your token at https://app.localstack.cloud/workspace/auth-token"; exit 1)
 	DOCKER_FLAGS='-e SF_LOG=trace' \
 	DEBUG=1 \
 	IMAGE_NAME=localstack/snowflake:latest \

README.md

@@ -24,12 +24,7 @@ The application implements a modern data pipeline architecture showcasing a real
 
 ## Prerequisites
 
-Features in this sample app require a LocalStack for Snowflake license - make sure your Auth Token is configured in your terminal session.
-
-```bash
-export LOCALSTACK_AUTH_TOKEN=<your-token>
-```
-
+- A valid [LocalStack for Snowflake license](https://localstack.cloud/pricing). Your license provides a [`LOCALSTACK_AUTH_TOKEN`](https://docs.localstack.cloud/getting-started/auth-token/) to activate LocalStack.
 - [Docker](https://docs.docker.com/get-docker/)
 - [`localstack` CLI](https://docs.localstack.cloud/getting-started/installation/#localstack-cli).
 - [AWS CLI](https://docs.localstack.cloud/user-guide/integrations/aws-cli/) with the [`awslocal` wrapper](https://docs.localstack.cloud/user-guide/integrations/aws-cli/#localstack-aws-cli-awslocal).