Tracking issue for installing rust without docs via rustup

[carols10cents]

Rustup tracking issue: rust-lang/rustup#998

If the ability to install without docs gets implemented, this spot will need to be updated: https://github.com/rust-lang-nursery/edition-guide/blame/68c458b9b68edced39aebea60e672a22d4d50edf/src/rust-2018/rustup-for-managing-rust-versions.md#L134-L136

This component cannot be removed for now; if that's of interest, please
comment on this issue.

[tesuji]

It is now possible with profile feature.

[ehuss]

Closing per #232, this section has been removed.

As mentioned, you can now skip docs with profiles. And there is now a rustup book with instructions on how to do various things.