Add README for Quarkus kafka template

[matthewpwilson]

Checklist:

• [x] Read the Code of Conduct and Contributing Guidelines.

• [x] Followed the commit message guidelines.

• [x] Stack adheres to Appsody stack structure.

Modifying an existing stack:

• [ ] Updated the stack version in stack.yaml - Not done as this is only a README change

As requested by @neeraj-laad I've added a specific README.md in the folder for the kafka template of the Quarkus stack. This keeps the details out of the main README.md and makes it consist with the other stacks.

[matthewpwilson]

@ianpartridge please review