docs: use shields.io badge (#2040)

Related to:
- https://github.com/simple-icons/simple-icons/pull/13593
- https://github.com/ratatui/ratatui/pull/1967

The Ratatui icon is available on shields.io now ✌️

And it's customizable. There are more configurations at
https://shields.io/badges.

Here are some examples:

```markdown
![](https://img.shields.io/badge/Ratatui-000?logo=ratatui&logoColor=fff)
![](https://img.shields.io/badge/Ratatui-fff?logo=ratatui&logoColor=000)
![](https://img.shields.io/badge/Built_With-Ratatui-000?logo=ratatui&logoColor=fff&labelColor=000&color=fff)
![](https://img.shields.io/badge/Ratatui-000?logo=ratatui&logoColor=fff&style=flat-square)
![](https://img.shields.io/badge/Ratatui-000?logo=ratatui&logoColor=fff&style=for-the-badge)
```

![](https://img.shields.io/badge/Ratatui-000?logo=ratatui&logoColor=fff)
![](https://img.shields.io/badge/Ratatui-fff?logo=ratatui&logoColor=000)

![](https://img.shields.io/badge/Built_With-Ratatui-000?logo=ratatui&logoColor=fff&labelColor=000&color=fff)

![](https://img.shields.io/badge/Ratatui-000?logo=ratatui&logoColor=fff&style=flat-square)

![](https://img.shields.io/badge/Ratatui-000?logo=ratatui&logoColor=fff&style=for-the-badge)

I also created a PR to the ratatui-website project to update the badge.
Here is the PR:

- https://github.com/ratatui/ratatui-website/pull/924

README.md

@@ -119,10 +119,10 @@ guidelines to ensure compliance.
 If you'd like to show your support, you can add the Ratatui badge to your project's README:
 
 ```md
-[![Built With Ratatui](https://ratatui.rs/built-with-ratatui/badge.svg)](https://ratatui.rs/)
+[![Built With Ratatui](https://img.shields.io/badge/Built_With_Ratatui-000?logo=ratatui&logoColor=fff)](https://ratatui.rs/)
 ```
 
-[![Built With Ratatui](https://ratatui.rs/built-with-ratatui/badge.svg)](https://ratatui.rs/)
+[![Built With Ratatui](https://img.shields.io/badge/Built_With_Ratatui-000?logo=ratatui&logoColor=fff)](https://ratatui.rs/)
 
 ## Acknowledgements