update changelog

Author: T4rk1n

CHANGELOG.md

@@ -6,6 +6,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ## Added
 - [#3395](https://github.com/plotly/dash/pull/3396) Add position argument to hooks.devtool
+- [#3403](https://github.com/plotly/dash/pull/3403) Add app_context to get_app, allowing to get the current app in routes.
 
 ## Fixed
 - [#3395](https://github.com/plotly/dash/pull/3395) Fix Components added through set_props() cannot trigger related callback functions. Fix [#3316](https://github.com/plotly/dash/issues/3316)