update changelog

Signed-off-by: Sotaro Hikita <bering1814@gmail.com>

Author: lawofcycles

CHANGELOG.md

@@ -3,9 +3,10 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ## [Unreleased]
 ### Added
+- Switched to more reliable OpenSearch Lucene snapshot location ([#597](https://github.com/opensearch-project/opensearch-hadoop/pull/597))
 
 ### Changed
-- Switched to more reliable OpenSearch Lucene snapshot location ([#597](https://github.com/opensearch-project/opensearch-hadoop/pull/597))
+- Add support for Amazon OpenSearch Serverless ([#586](https://github.com/opensearch-project/opensearch-hadoop/pull/586))
 
 ### Deprecated