docs: rust: remove unintended blockquote in Quick Start

Remove indentation within the "Hacking" section of the Rust Quick Start
guide, i.e. remove a `<blockquote>` HTML element from the rendered
documentation.

Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: https://github.com/Rust-for-Linux/linux/issues/1103


Fixes: d07479b2 ("docs: add Rust documentation")
Signed-off-by: Jon Mulder <jon.e.mulder@gmail.com>
Link: https://lore.kernel.org/r/20240826-pr-docs-rust-remove-quickstart-blockquote-v1-1-c51317d8d71a@gmail.com


[ Added Fixes tag, reworded slightly and matched title to a previous,
  similar commit. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>