Document rust-lang/rust CI artifact naming conventions

[jieyouxu]

Summary

It is my understanding as well that rustc/ prefix for artifact name by convention means that it is used by rust-lang/rust CI. So actually document this to make it explicit.

cf. #47 (review).

[marcoieni]

is this convention something that makes sense? Or is it how things happened to be?
I wonder if we should establish a better convention and move files in different directories accordingly.

(in other PRs)

[Kobzol]

We could also add some code check that entries within a directory follow some convention based on that directory.

[jieyouxu]

is this convention something that makes sense? Or is it how things happened to be? I wonder if we should establish a better convention and move files in different directories accordingly.

The existence of this predates my time, it's less of an actual convention and more of a "this is how things happened to be" AFAIK.

We don't need to merge this now, we can see if there's a more deliberate organization then just move artifacts to a better structure if we come up with one. (In fact that's probably much better, so I'll mark this as draft.)

EDIT: rust-lang/infra-team#286