Document the edition2024 code block attribute

Author: noritada

guide/src/format/configuration/general.md

@@ -73,7 +73,7 @@ edition = "2015"   # the default edition for code blocks
 
 - **edition**: Rust edition to use by default for the code snippets. Default
   is `"2015"`. Individual code blocks can be controlled with the `edition2015`,
-  `edition2018` or `edition2021` annotations, such as:
+  `edition2018`, `edition2021` or `edition2024` annotations, such as:
 
   ~~~text
   ```rust,edition2015

guide/src/format/mdbook.md

@@ -122,7 +122,7 @@ These use the same attributes as [rustdoc attributes], with a few additions:
 * `no_run` --- The code is compiled when tested, but it is not run.
   The play button is also not shown.
 * `compile_fail` --- The code should fail to compile.
-* `edition2015`, `edition2018`, `edition2021` --- Forces the use of a specific Rust edition.
+* `edition2015`, `edition2018`, `edition2021`, `edition2024` --- Forces the use of a specific Rust edition.
   See [`rust.edition`] to set this globally.
 
 [`mdbook test`]: ../cli/test.md