feat(ui): about page

[ArcticLampyrid]

Slint 以三种方式提供使用许可：

1. Royalty-free license （此选项不适用于嵌入式应用）
2. GNU GPLv3
3. Paid license （商业授权）

本项目使用 MIT License，不符合选项 2。根据选项 1 的法律要求，我们需要在软件的关于页面和项目主页等位置添加 MadeWithSlint 徽标。

You may distribute the Software as part of an Application, modified or unmodified, provided that You do either of the following:

(a) Display the AboutSlint widget in an "About" screen or dialog that is accessible from the top level menu of the Application. In the absence of such a screen or dialog, display the widget in the "Splash Screen" of the Application.

(b) Display the Slint attribution badge on a public webpage, preferably where the binaries of your Application can be downloaded from, in such a way that it can be easily found by any visitor to that page.

[Serein207]

有关于页面的设计，会放上去的 😄