📝 docs(CHANGELOG): add initial changelog file

- create CHANGELOG.md to document notable changes
- follow Keep a Changelog format and Semantic Versioning standards

CHANGELOG.md

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+<!-- LTex: Enabled=false -->
+# 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/1.0.0/) and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased] - 
+
+Summary: Added[4], Build[3], Chore[19], Continuous Integration[4], Documentation[6]
+
+### Added
+
+ - ✨ feat(vscode): add custom dictionary entry for ltex
+ - ✨ feat(assets): add new logo and splash screen
+ - ✨ feat(lib): add addition function with test
+ - ✨ feat(project): add initial Cargo.toml for cull-gmail tool
+
+[Unreleased]: https://github.com/jerus-org/cull-gmail/commits/main/
+