add initial changelog

CHANGELOG.md

+# 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).
+
+Dates are displayed in the format YYYY-MM-DD.
+
+## [Unreleased]
+
+## [0.1.0] - 2024-01-12
+
+### Added
+
+- Initial release of HARMONY & EIFFEL
+- Default templates for PARIS (PAtterns for RequIrements Specification) by Oliver Linssen (see [README.md](README.md))
+- EIFFEL (app/eiffel) for requirements elicitation
+- Functionality for creating, editing and deleting templates and template sets (for grouping templates)
+- Functionality for OAuth2 login with GitHub and Google
+- Functionality for editing user information
+- Main command for running the application as a web server
+- Migrations command with initial migration for creating database schema
+- Lots and lots of [core](src/core) functionality containing utilities
+- Docker setup for production deployments
+- HTMX and Bootstrap 5 for frontend
+- Translations of the frontend to German and English
+- Vendorized dependencies for Go backend (frontend is in public/assets)