Hello cargo

Built on top of https://github.com/rust-lang/rust/pull/15181. https://github.com/steveklabnik/rust/commit/e52719291183d7b4f691a1997c69fd75b8101b07 is the only new commit, you may want to review that separately.

I'm not sure if the car analogy is too glib.
Ick, “here”. I’d prefer it to be something like

    The easiest is [the #rust IRC channel on
    irc.mozilla.org](irc://irc.mozilla.org/#rust), which you can access through
    [Mibbit](http://chat.mibbit.com/?server=irc.mozilla.org&channel=%23rust).

It’s still a little clumsy, but generally better. The `irc://` link could be omitted too, though I personally would prefer such a thing to be there.