Add Dotter.gitnore

[barraponto]

Reasons for making this change

[Dotter][https://github.com/SuperCuber/dotter] is a dotfiles manager tool written in Rust.
Its setup guide recommends ignoring local override files and the default cache files.

Links to documentation supporting these rule changes

https://github.com/SuperCuber/dotter/wiki/Setup-and-Configuration

If this is a new template

Link to application or project’s homepage: https://github.com/SuperCuber/dotter

Merge and Approval Steps

• Confirm that you've read the contribution guidelines and ensured your PR aligns
• Ensure CI is passing
• Get a review and Approval from one of the maintainers