Added changelog

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/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [unreleased]
+
+_Nothing as of yet_
+
+## [v1.0.0] - 2022-07-31
+
+### Added
+
+- First version of the action
+  - Grabs the Data Dragon versions index and picks the first patch number via regex
+  - Patch number is saved in an output variable for further usage
+  - Will fail if Data Dragon can't be reached or if patch number seems invalid
+- Changelog
+- Readme
+- MIT License
+
+[//]: # 'Links to releases:'
+[unreleased]: https://github.com/marvinscham/get-league-patch/compare/v1.0.0...main
+[v1.1.0]: https://github.com/marvinscham/get-league-patch/compare/v1.0.0...v1.1.0
+[v1.0.0]: https://github.com/marvinscham/get-league-patch/commits/v1.0.0