Make an example rustpkg repository under github.com/rust-lang

[catamorphism]

Currently, the rustpkg tutorial uses a test repository under @steveklabnik 's account to illustrate an example git package, but that's not ideal. I should make one under /mozilla (though I have to figure out how to do that).

[kud1ing]

Maybe https://github.com/rust-lang is the best place.

[huonw]

Triage, no change, and yes, /rust-lang would be better (changed the title).

[alexcrichton]

rustpkg is gone