docs: add features

Author: marjune163

README.md

@@ -6,6 +6,7 @@ Simple command line based HTTP file server to share local file system.
 ## Features
 - More friendly UI than Apache/Nginx directory index page
 - Adapt for mobile display
+- Single executable file
 - Can download the whole contents of current directory as archive file if enabled
 - Can upload files to current directory if enabled
 - Can specify a custom template for page rendering

README.zh-CN.md

@@ -6,6 +6,7 @@
 ## 软件特色
 - 比Apache/Nginx更友好的目录列表
 - 适配移动设备显示
+- 单一可执行文件
 - 可以将当前浏览目录内容打包下载
 - 可以开启某个目录的上传权限
 - 可以指定自定义模板来渲染页面