add changelog

CHANGELOG

+# 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).
+
+## [0.1.0] - 2018-08-22
+
+### Added
+- This fine changelog
+
+### Changed
+- the structure of `src/nf_modules`: the `tests` folder was removed
+
+### Removed
+- nothings
+