Add more examples of autocmds and NoAutoFormatBuffer to help

Would be nice to have some practical examples in the docs of how to:
- Auto-format some filetype excluding certain paths.
- Configure default formatter by filetype w/o enabling auto-format.
- Auto-format w/ different formatters at different paths.
- Auto-format but manually disable in some buffers with `:NoAutoFormatBuffer`.

首先找到关于 autocmds 和 :NoAutoFormatBuffer 的现有文档，然后将其中当前的指导与 issue 中列出的四种场景进行比较。添加涵盖路径排除、按文件类型设置默认 formatter、特定路径的 formatter 以及手动禁用 buffer 的实用示例；当四种用例都得到清晰记录后即可完成。

由索引模型根据 Issue 内容生成。