docs: add Unreleased section to changelog

Author: daniel-jones-dev

CHANGELOG.md

@@ -5,6 +5,15 @@ 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]
+### Added
+### Changed
+### Deprecated
+### Removed
+### Fixed
+### Security
+
+
 ## [1.8.0] - 2022-06-10
 ### Added
 * Optional `filename` parameter added to `Translator.translate_document()`, only
@@ -177,6 +186,7 @@ Version increased to avoid conflicts with old packages on PyPI.
 Initial version.
 
 
+[Unreleased]: https://github.com/DeepLcom/deepl-python/compare/v1.8.0...HEAD
 [1.8.0]: https://github.com/DeepLcom/deepl-python/compare/v1.7.0...v1.8.0
 [1.7.0]: https://github.com/DeepLcom/deepl-python/compare/v1.6.0...v1.7.0
 [1.6.0]: https://github.com/DeepLcom/deepl-python/compare/v1.5.1...v1.6.0