update docs

CHANGELOG_CN.md

@@ -5,6 +5,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ## [Unreleased]
 
+### Added
+- 移除播放器 UI 初始化的 video:loadedmetadata 事件
+- 弹幕库暴露 load 方法，用于切换弹幕源
+
 ## [4.4.1] - 2022-05-17
 
 ### Added