add Artplayer.SEEK_STEP

CHANGELOG_CN.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+- 新增 `Artplayer.VOLUME_STEP` 用于控制调整 `音量` 的步长，默认为 `0.1`
+- 新增 `Artplayer.SEEK_STEP` 用于控制调整 `快进/快退` 的步长，默认为 `5` 秒
 
 ## [4.5.6] - 2022-9-19
 - 修复 `hls.js` 在 `Safari` 播放失效的问题