docs: rust: quick-start: add Ubuntu

docs: rust: quick-start: add Ubuntu

Ubuntu has changed their maintenance model for Rust toolchains and is
now providing recent Rust releases in their releases, including both
LTS and non-LTS (interim) releases.

Therefore, add instructions to the Quick Start guide for Ubuntu, like
it is done for the other distributions.

Link: https://packages.ubuntu.com/search?keywords=rustc-1
Link: https://packages.ubuntu.com/search?keywords=bindgen-0
Cc: Zixing Liu <zixing.liu@canonical.com>
Cc: William Grant <wgrant@ubuntu.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20240925140600.275429-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>