Add changelog

Author: Erdenezul Batmunkh

docs/changelog.rst

@@ -23,6 +23,7 @@ Development
     - Calling `connect` 2 times with the same alias and different parameter will raise an error (should call `disconnect` first).
     - `disconnect` now clears `mongoengine.connection._connection_settings`.
     - `disconnect` now clears the cached attribute `Document._collection`.
+- BREAKING CHANGE: `EmbeddedDocument.save` & `.reload` is no longier exist #1552
 - (Fill this out as you fix issues and develop your features).
 
 Changes in 0.17.0