Add CHANGELOG.md to document project updates and version history

- Introduced a new CHANGELOG.md file to track notable changes in the project.
- Documented the initial release (1.0.0) with details on added features, documentation improvements, and licensing information.
- Adheres to the Keep a Changelog format and Semantic Versioning.

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [1.0.0] (2026-02-06)
+
+### Added
+
+- Custom checkbox list field for Strapi v5 Content Type Builder
+- Multi-select interface with intuitive checkbox-based selection
+- Flexible configuration for defining custom option lists per field instance
+- Native integration with Strapi's Content Type Builder
+- Full TypeScript support for type-safe development
+- Playground environment for development and testing
+- Watch mode for active development with automatic rebuilds
+- Plugin linker support for local development workflow
+
+### Documentation
+
+- Comprehensive README with installation and usage instructions
+- Development setup guide for contributors
+- MIT License
+
+[1.0.0]: https://code.popov.link/valentineus/strapi-plugin-checkbox-list/releases/tag/v1.0.0