add 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/).
+
+## [Unreleased]
+
+## [8.11.0] - 2020-05-27
+### Added
+- Support for building with dune, including extraction of OCaml code
+- Metadata on project, including detailed publication information
+
+### Fixed
+- Compatibility with Coq 8.11
+
+### Changed
+- Reorganize files into subdirectories
+- Generalize definitions and results from Set to Type
+
+[Unreleased]: https://github.com/coq-community/chapar/compare/v8.11.0...master
+[8.11.0]: https://github.com/coq-community/chapar/releases/tag/v8.11.0