docs: set requirement in README

Author: ddevsr

README.md

@@ -6,6 +6,10 @@
 
 See available [Codeigniter4 rules](/docs/rector_rules_overview.md)
 
+## Requirement
+
+This package initiated, CodeIgniter for `4.5` already prepare rector with minimum PHP 8.1. And we follow minimum PHP 8.1 for the future.
+
 ## Install
 
 This package is a [Rector](https://github.com/rectorphp/rector) extension developed by the Laravel community.