[splitter]add change log

Author: Yi, Jihyeon

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Added
+- Task-specific Splitter (<https://github.com/openvinotoolkit/datumaro/pull/68>)
 - `WiderFace` dataset format (<https://github.com/openvinotoolkit/datumaro/pull/65>)
 - Function to transform annotations to labels (<https://github.com/openvinotoolkit/datumaro/pull/66>)