"cargo --list" will show all commands, which shows fetch. "cargo fetch --help" then shows the help for fetch.

We certainly have some work to do on Cargo's docs. Please don't hesitate to open a thread on users.rust-lang.org if you run into some kind of issue. In addition, I actually live in Brooklyn; if Pivotal ever needs a hand with Rust stuff, just let me know, I'd be happy to swing by your office and talk about whatever.