Update CHANGELOG-5.1.md

Author: XWB

CHANGELOG-5.1.md

@@ -13,6 +13,7 @@ in 5.1 versions.
 * Added refresh options for persisters.
 * Added index name to `TransformEvent` document.
 * Added many unit tests.
+* Added index templates support.
 * Change method visibility in `Configuration` to private.
 * Handle multiline strings in `ElasticaLogger`.
 * Fixed pagination of ORM queries when populating.