chore: update example of registering an event source

[matteriben]

Updated the example of registering an event source and also the link.

Previous example:

• Returned List instead of Map
• Used name configMapEventSource , but was apparently for Deployment
• Had apparent copy/paste error around lines 508-509

Updated example:

• Omits some details of the actual linked code
• Increased indentation

[metacosm]

Thank you!