Update Zoxide shell setup for Nushell in README

[Rikiub]

Auto-load files support was added on Nushell v0.96.0, allowing nu files to be auto-loaded on shell start. This behavior is documented here.

This PR replaces the need of have a separate file and source it "manually". Instead, Zoxide completions now can be added with one-line command.

Also, Zoxide now requires v0.96.0+ as minimum Nushell version.

[ajeetdsouza]

Unfortunately, this wouldn't work.

The reason zoxide requires you to add zoxide init nushell | save -f ~/.zoxide.nu to your Nushell env file is so that the init script is regenerated every time you start a new shell. The advantage of this approach is that every time you update zoxide, the init script gets updated.

Given how often Nushell introduces breaking changes, it is important to make this process smooth. The only other option would be to expect the user to remember to re-run the init script every time they update zoxide, which would be bad UX.

[Rikiub]

Thanks for the advice, I made some changes.

Now requires write the command inside config.nu, so each time the shell is started, the file autoload/zoxide.nu is created.

I think should be enough @ajeetdsouza