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
+
+
 ## [1.3.1] - 2021-11-15
 ### Changed
 * Limit document status update wait time to 60 seconds, and log wait times.
@@ -108,6 +117,7 @@ Version increased to avoid conflicts with old packages on PyPI.
 Initial version.
 
 
+[Unreleased]: https://github.com/DeepLcom/deepl-python/compare/v1.3.1...HEAD
 [1.3.1]: https://github.com/DeepLcom/deepl-python/compare/v1.3.0...v1.3.1
 [1.3.0]: https://github.com/DeepLcom/deepl-python/compare/v1.2.1...v1.3.0
 [1.2.1]: https://github.com/DeepLcom/deepl-python/compare/v1.2.0...v1.2.1