PackageMerging examples out of date?

[s-makin]

The PackageMerging.md page uses Cosmic and Disco in the examples throughout - at one point it even says "Disco is not available yet at time of writing", which is why I first noticed this. This makes the entire page feel out of date and neglected.

I think that if it's possible, these examples should be made as generic as possible (or at least brought up to date with e.g. Jammy/Focal).