tree生成目录树

        生成目录结构，使用tree命令：

    tree

        只包含目录，不包含文件：

    └─src
        └─main
            ├─java
            │  └─cn
            │      └─quibbler
            │          └─demo
            └─res
                ├─drawable
                ├─drawable-v24
                ├─layout
                ├─mipmap-anydpi-v26

        生成树状文件结构：

    tree /F

        示例：

    └─src
        └─main
            │  AndroidManifest.xml
            │
            ├─java
            │  └─cn
            │      └─quibbler
            │          └─demo
            │                  DemoActivity.kt
            │                  GridAdapter.kt
            │
            └─res
                ├─drawable
                │      ic_launcher_background.xml
                │
                ├─drawable-v24
                │      ic_launcher_foreground.xml
                │
                ├─layout
                │      activity_demo.xml
                │      cricle_item.xml
                │
                ├─mipmap-anydpi-v26
                │      ic_launcher.xml
                │      ic_launcher_round.xml

        将目录的结构以树状形式输出到文件tree.txt中

    tree /F > tree.txt