Improve docs around layers/rechunking

[jeckersb]

This information somewhat exists currently but it's scattered in a few places and is more focused on the "how" than the "why". We should have a clear document that explains how container layers work in general, how they work specifically with bootc images, and when and why one might want to rechunk a bootc image.

[cgwalters]

We should have a clear document that explains how container layers work in general

Why would that be part of this project as opposed to us referencing existing docs?

and when and why one might want to rechunk a bootc image.

Today though that's the domain of external tools. I think this really best lives in the Fedora bootc docs (and of course the RHEL docs).

At least until of course as you know https://github.com/jlebon/chunkah matures.

[jeckersb]

We should have a clear document that explains how container layers work in general

Why would that be part of this project as opposed to us referencing existing docs?

Well most of that is probably just linking to the right places. But also the existing docs I imagine are a bit too exhaustive (I haven't actually looked) and we probably also want to summarize it a bit so the information is as useful and concise as possible. I know at least for me I would rather read a curated, information-dense version instead of reading through the exhaustive version and trying to understand which are the more important and relevant parts.