Document promoting a bundle use case

[DennisDenuto]

Describe the problem/challenge you have I wanted to know how to use imgpkg when promoting a bundle between various environments (dev->qa->prod). And have a deeper understanding on how imgpkg pull with imgpkg copy helps with this.

Describe the solution you'd like A new scenario added to help demonstrate this

Note: Would be useful to have diagrams to help communicate this. such as https://jvns.ca/blog/2017/06/04/learning-about-kubernetes/

cc/ @iamhsk

[joaopapereira]

This sounds like valuable documentation to have in carvel.dev

Going to accept the story