Merge pull request #4196 from rust-lang/appendix-e-2024-edition

Appendix E: Update for 2024 Edition

Author: chriskrycho

src/appendix-05-editions.md

@@ -24,8 +24,9 @@ Editions serve different purposes for different people:
 - For those developing Rust, a new edition provides a rallying point for the
   project as a whole.
 
-At the time of this writing, three Rust editions are available: Rust 2015, Rust
-2018, and Rust 2021. This book is written using Rust 2021 edition idioms.
+At the time of this writing, four Rust editions are available: Rust 2015, Rust
+2018, Rust 2021, and Rust 2024. This book is written using Rust 2024 edition
+idioms.
 
 The `edition` key in _Cargo.toml_ indicates which edition the compiler should
 use for your code. If the key doesn’t exist, Rust uses `2015` as the edition