Update README.md

Author: lam0819

README.md

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 A powerful, framework-agnostic workflow engine for PHP applications. This core library provides comprehensive workflow definition, execution, and state management capabilities without any framework dependencies.
 
+> ⚠️ **WARNING: DEVELOPMENT STATUS**⚠️ 
+> 
+> This package is currently under active development and is **NOT READY FOR PRODUCTION USE**. 
+> 
+> Features may be incomplete, APIs might change, and there could be breaking changes. Use at your own risk in development environments only.
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 ## 📋 Requirements
 
 - **PHP 8.3+** - Leverages modern PHP features for type safety and performance