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>

Documentation/rust/quick-start.rst

@@ -87,6 +87,23 @@ they should generally work out of the box, e.g.::
 	zypper install rust rust1.79-src rust-bindgen clang
 
 
+Ubuntu
+******
+
+Ubuntu LTS and non-LTS (interim) releases provide recent Rust releases and thus
+they should generally work out of the box, e.g.::
+
+	apt install rustc-1.80 rust-1.80-src bindgen-0.65 rustfmt-1.80 rust-1.80-clippy
+
+``RUST_LIB_SRC`` needs to be set when using the versioned packages, e.g.::
+
+	RUST_LIB_SRC=/usr/src/rustc-$(rustc-1.80 --version | cut -d' ' -f2)/library
+
+In addition, ``bindgen-0.65`` is available in newer releases (24.04 LTS and
+24.10), but it may not be available in older ones (20.04 LTS and 22.04 LTS),
+thus ``bindgen`` may need to be built manually (please see below).
+
+
 Requirements: Building
 ----------------------