Update faq for fetching rust source.
Update faq for fetching rust source.

nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,nodakai/rustup.rs,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,rust-lang/rustup,rust-lang/rustup,rust-lang/rustup