Clarify "call site hierarchy" in macro

[Arthur-Milchior]

I'd appreciate if you could clarify, in https://rustc-dev-guide.rust-lang.org/macro-expansion.html , the part about call site hierarchy. Giving an example with a non-trivial hierarchy may suffices. But right now, I admit I've no idea what it means. And why this is compared to the first hierarchy. It's even stranger, because the text mentions the hierarchy of macro invocation, but it considers the hierarchy of baz which is not a macro