Use the correct name for the service in the readme

[skounis]

In the readme.md we read

• Describe the load balanced service:
  kubectl describe services hello-python-service

However in kube-hello-change.yaml the name of service is hello-flask-change-service

apiVersion: v1
kind: Service
metadata:
  name: hello-flask-change-service

The correct command is

kubectl describe services hello-flask-change-service