docs: update PHP 8 requirements

Author: williamdes

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased] - yyyy-mm-dd
 
-- Drop PHP 7.4, PHP 8.0
+- Drop PHP 7.4, PHP 8.0, require PHP >= `8.1`
 - Attempt to reload the current page in a newly-selected version
 - Support PHPUnit 10, 11 and 12
 - Drop PHPUnit 7 and 8

README.rst

@@ -23,7 +23,7 @@ Installation
 
 .. caution::
 
-    Doctum requires **PHP 7.2.20** or later.
+    Doctum requires **PHP 8.1** or later.
 
 Get Doctum as a `phar file`_: