Add the best use case example for different Knative Features

[Leo6Leo]

Description

There's a need for practical examples to better understand the use cases of Knative's components. The questions such as when will be the best time to use Knative Service? What situation would not be a good idea to use it? What are the best examples to use it?...

For example, you may not want to use Knative service to deploy a database that aren't HTTP request based.

This could better help the users to connect their current existing applications, and allow them to make connections between Knative and the gap in their application.

Expected Outcomes

• Examples illustrating best practices for using Knative components.

[jasonsmithio]

/assign