Meta: Switch to clang-format-20 as the standard formatter

Author: https://github.com/trflynn89
Commit: d30f6f1b11
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4715
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/BertalanD
Reviewed-by: https://github.com/InvalidUsernameException

Documentation/CodingStyle.md

@@ -2,7 +2,12 @@
 
 For low-level styling (spaces, parentheses, brace placement, etc), all code should follow the format specified in `.clang-format` in the project root.
 
-**Important: Make sure you use `clang-format` version 19!**
+**Important: Make sure you use the correct version of `clang-format`!**
+
+See [lint-clang-format.sh](../Meta/lint-clang-format.sh) for the version enforced in CI.
+
+See [AdvancedBuildInstructions.md](AdvancedBuildInstructions.md#clang-format-updates) for instructions on how to get an
+up-to-date version if your OS distribution does not ship the correct version.
 
 This document describes the coding style used for C++ code in the Ladybird Browser project. All new code should conform to this style.