Updates changelog

Author: nunomaduro

CHANGELOG.md

@@ -6,6 +6,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 # Release Notes
 
+## [Unreleased]
+
+### Fixed
+- Batching algorithm when reaching the `batch_size`. ([#421](https://github.com/algolia/algoliasearch-client-python/pull/421))
+
 ## [v2.0.0](https://github.com/algolia/algoliasearch-client-python/compare/1.20.0...2.0.0)
 
 ### Changed