Add short application description under name on all help screens

Currently if I type application name help screen does not contain any short description of application. If I use help on windows dir command:
```
`C:\Users\Example>dir /?
Displays a list of files and subdirectories in a directory.

...help text continues
```
I think that it's nice way of communicating for user, what this tool does (in few words).

Current output:
```
>MyApp.exe
MyApp 1.0.0
Copyright (C) 2018 MyApp

verb1 Help text for verb 1
verb2 Help text for verb 2
help Display more information on a specific command.
version Display version information.
```

Would be nice output:
```
>MyApp.exe
MyApp 1.0.0
Utility for mass renaming files
Copyright (C) 2018 MyApp

verb1 Help text for verb 1
verb2 Help text for verb 2
help Display more information on a specific command.
version Display version information.
```

I think System.Reflection.AssemblyDescriptionAttribute would be good source of this description.

首先追蹤應用程式的頂層說明畫面是如何組裝的，以及應用程式名稱、版本和版權資訊寫入的位置。檢查那裡是否可以使用 System.Reflection.AssemblyDescriptionAttribute 作為描述來源。完成的標準是：簡短描述顯示在所有相關說明畫面的名稱下方，同時不影響現有的命令說明和版本說明。

由索引模型根據 Issue 內容生成。