doc: create a CHANGELOG.md file

CHANGELOG.md

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+# Changelog
+
+All notable changes to the project will be documented in this file. It is meant for humans to read.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+
+## Unreleased
+
+Nothing is released yet, the application is in the design phase.