message: Add rustup link
diff: ### Install Rust and Cargo
  The easiest way to get Cargo is to install the current stable release of [Rust]
  -by using `rustup`. Installing Rust using `rustup` will also install `cargo`.
  +by using [rustup]. Installing Rust using `rustup` will also install `cargo`.
  On Linux and macOS systems, this is done as follows:
  @@ -32,6 +32,7 @@ For other installation options and information, visit the
  Alternatively, you can [build Cargo from source][compiling-from-source].
  [rust]: https://www.rust-lang.org/
  +[rustup]: https://rustup.rs/
  [rustup-init.exe]: https://win.rustup.rs/
  [install-rust]: https://www.rust-lang.org/tools/install
  [compiling-from-source]: https://github.com/rust-lang/cargo#compiling-from-source
  