Merge pull request #9138 from kenjis/docs-php-version-and-ci4-version

[4.6] docs: add note about PHP versions supported by CI4 versions

Author: kenjis

user_guide_src/source/intro/requirements.rst

@@ -19,9 +19,16 @@ PHP and Required Extensions
 .. warning::
     - The end of life date for PHP 7.4 was November 28, 2022.
     - The end of life date for PHP 8.0 was November 26, 2023.
-    - If you are still using PHP 7.4 or 8.0, you should upgrade immediately.
+    - **If you are still using PHP 7.4 or 8.0, you should upgrade immediately.**
     - The end of life date for PHP 8.1 will be December 31, 2025.
 
+.. note::
+    - PHP 8.4 requires CodeIgniter 4.6.0 or later.
+    - PHP 8.3 requires CodeIgniter 4.4.4 or later.
+    - PHP 8.2 requires CodeIgniter 4.2.11 or later.
+    - PHP 8.1 requires CodeIgniter 4.1.6 or later.
+    - **Note that we only maintain the latest version.**
+
 ***********************
 Optional PHP Extensions
 ***********************