Document container layering

[meadsteve]

Lagom allows (and should encourage) containers to be stacked on top of each other. This is especially useful when you have different contexts like a web app and a worker on some job queue that share some dependency construction logic but not all.

[mgodkowicz]

@meadsteve Hi, could you please elaborate on that? Did you mean container parameter in Container class? Or maybe there's another way to have multiple small containers, per module, that could be connected as one?