Render the book to PDF and make it available for download

Hey there, @max-heller was a great help to comprehensive-rust and rust-patterns as they helped us set up rendering to PDF. So what's your opinion on having the book available as a nice looking PDF?

mdbook-pandoc has some pre-rendered examples in also of Rust-by-example and the book: https://github.com/max-heller/mdbook-pandoc?tab=readme-ov-file#rendered-books

• Comprehensive Rust: https://google.github.io/comprehensive-rust/comprehensive-rust.pdf

• Rust Design Patterns: https://rust-unofficial.github.io/patterns/rust-design-patterns.pdf

(At this point, I think it makes sense to write up a condensed tutorial how to add PDF support to an existing mdbook...)

Some Resources

• Initial support PR: https://github.com/rust-unofficial/patterns/pull/394

• Adding download icon to menu bar: https://github.com/rust-unofficial/patterns/commit/d96de404c45f17310c3eb77b4669d715ce923d33

• Line wrapping in code blocks: https://github.com/rust-unofficial/patterns/commit/3dd157b9d751e2a5a391b2933ae6eb8467ea1eaf

• Readme of mdbook-pandoc: https://github.com/max-heller/mdbook-pandoc?tab=readme-ov-file#getting-started