[tutorial] Recommend more refined explanation of its purpose

[DazWilkin]

I followed the tutorial.

I think it would benefit from a more precise explanation of what it shows | what is solved by Service Catalog. IIUC for Cloud Pub/Sub, Service Catalog enables the provisioning of Pub/Sub resources (perhaps "topics" only). This is useful.

It is not evident from the tutorial that this is the benefit. The tutorial merges the creation of the topic (by the Service Catalog) with the creation of a service account for the Kubernetes app, the deployment of the Kubernetes app etc.

I think perhaps a before-then-after scenario would help:

1. Here's how you'd bind a Pub/Sub client to a GCP Pub/Sub topic without Service Catalog
2. Here's how Service Catalog simplifies (albeit rather trivially) this process.
3. You've seen how this works for Pub/Sub, you can how this could generalize for other services!