First App Experience doc: Be explicit about which "properties" to edit

[Reshrahim]

Summary

Captured as part of a usability study with first-app experience

When adding a Redis cache, there are two "properties": one in the app block and one in the Redis cache block

Proposed action

Make the docs explicit that the customer needs to edit the property in the Redis cache block

AB#8884

[willtsai]

This feedback is common, best solution would probably be some sort of mechanism to highlight diffs in the code blocks to show users exactly where to add the code.

[Reshrahim]

completed by #684