update changelog

Author: namusyaka

CHANGELOG.md

@@ -9,7 +9,12 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
-
+- `peering_completed` marker to postgresql module [#43]
+- `private_address` to postgresql module [#43]
 
 ### Changed
 
+- the root module has been deprecated [#56]
+
+[#56]: https://github.com/terraform-google-modules/terraform-google-sql-db/pull/56
+[#43]: https://github.com/terraform-google-modules/terraform-google-sql-db/pull/43