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`.

Start by locating the existing documentation for autocmds and :NoAutoFormatBuffer, then compare its current guidance with the four scenarios listed in the issue. Add practical examples covering path exclusions, per-filetype default formatters, path-specific formatters, and manual buffer disabling; done means all four use cases are documented clearly.

Written by the indexing model from the issue text.