Filter tmp dir by default

[elkesrio]

Hello,
Thank you for this plugin, it works like a charm 🙏

I had a problem of slowness in my Neovim right after running a test via neotest-rspec caused by not the scan of my huge tmp directory (more than 1k folder inside tmp/storage).
I think, I'm not the only one having this problem.

To prevent this for future users, I suggest these two options:

1. Add tmp to this line to filter tmp by default
2. Add a paragraph about this problem in the documentation

WDYT ?

If you're open to PRs, I can create one.

Thanks,

[olimorris]

This would be a very sensible addition to the plugin. Please submit a PR.