changelog entry for 660 - Dropdown.search_value

Author: alexcjohnson

CHANGELOG.md

@@ -2,6 +2,10 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+### Added
+- Added `search_value` prop to `Dropdown`, for server-side options loading/filtering. [#660](https://github.com/plotly/dash-core-components/pull/660)
+
 ## [1.2.1] - 2019-09-19
 ### Fixed
 - Fix regression in DatePickerRange, DatePickerSingle, Input