Update CHANGELOG.md

Author: andrextor

CHANGELOG.md

@@ -7,4 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- added: adds authentication module
+### Added
+
+- Initial release of Checkout P2P version 1.0.0.
+- Support for **query**, **single payments**, **subscriptions**, **payments using subscription tokens** and **reverse**.
+- Added Pydantic-based validation for request and response models.
+- Decorators to format booleans and clean dictionaries for API compatibility.