docs(README): update clone instruction

Signed-off-by: Tianling Shen <[email protected]>

README.md

@@ -19,7 +19,7 @@
     #进入 OpenWrt 源码 package 目录
     cd package
     #克隆插件源码
-    git clone https://github.com/UnblockNeteaseMusic/luci-app-unblockneteasemusic.git
+    git clone --branch master https://github.com/UnblockNeteaseMusic/luci-app-unblockneteasemusic.git
     #返回上一层目录
     cd ..
     #配置