Document how to delete the deployment

[simonw]

After trying this out (as a very new-to-Kubernetes person) I had a lot of trouble figuring out how to remove it again.

Eventually this worked for me:

kubectl delete deployment hello-kubernetes-hello-world -n hello-kubernetes

Would be great if the README covered this!

[dcorbe]

The correct way to uninstall a helm chart is to use helm uninstall RELEASE_NAME where RELEASE_NAME is the name you gave to your application at installation time. If you can't remember the name of the release, run helm list