helm-guestbook example cleanup

The helm-guestbook example works as expected using the following commands:

```
argocd app create helm-guestbook --repo https://github.com/argoproj/argocd-example-apps --path helm-guestbook --dest-name in-cluster --dest-namespace default

argocd app sync helm-guestbook

kubectl port-forward svc/guestbook-helm-guestbook 8080:80 -n default
```

The example should provide some documentation on the above commands and should also illustrate something unique about argo-cd's helm support. Maybe the values-production.yaml file should be updated and used as part of the example or an update can be pushed to the values file to show the change synced in.

Start with the helm-guestbook example and its values-production.yaml file, then run the documented argocd app create, argocd app sync, and kubectl port-forward commands. Clarify which Helm-specific behavior the example should demonstrate, document the workflow, and ensure the production values or a values change is used and visibly synced.

Written by the indexing model from the issue text.