Going through the guestbook tutorial for the first time,
the deployment configuration mentioned that whether my configuration
included a DNS service would dictate which env value I used for the
`GET_HOSTS_FROM` variable. According to
https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/,
k8s includes DNS by default starting with v1.3.
Add this additional info to help the user better understand when DNS
may/may not be enabled.
Matt McNaughton
Ahmet Alp Balkan