Slightly different `rustup` instructions compared to rust-lang.org's Install page

[Miguel Ojeda]

The instructions for rustup:

rust-forge/src/infra/other-installation-methods.md

Line 54 in 40d4682

 - On Unix, run `curl https://sh.rustup.rs -sSf | sh` in your shell. This 

rust-forge/src/infra/other-installation-methods.md

Line 65 in 40d4682

 curl https://sh.rustup.rs -sSf | sh -s -- --help 

are slightly different from what it is shown in rust-lang.org's Install page:

https://github.com/rust-lang/www.rust-lang.org/blob/c50cd2f9b53fe04c68a9f7fd5fc5899c5e808a6e/templates/components/tools/rustup.html.hbs#L20