Update getting-started.md

In `rustc 1.7.0` the message that is displayed is now `Rust is ready to roll.`

Author: naltun

src/doc/book/getting-started.md

@@ -119,19 +119,7 @@ This will download a script, and start the installation. If it all goes well,
 you’ll see this appear:
 
 ```text
-Welcome to Rust.
-
-This script will download the Rust compiler and its package manager, Cargo, and
-install them to /usr/local. You may install elsewhere by running this script
-with the --prefix=<path> option.
-
-The installer will run under ‘sudo’ and may ask you for your password. If you do
-not want the script to run ‘sudo’ then pass it the --disable-sudo flag.
-
-You may uninstall later by running /usr/local/lib/rustlib/uninstall.sh,
-or by running this script again with the --uninstall flag.
-
-Continue? (y/N)
+Rust is ready to roll.
 ```
 
 From here, press `y` for ‘yes’, and then follow the rest of the prompts.