Document or set the recursive strategy as default with --use-on-cd

[NicolasWebDev]

I had been waiting for #607 to be merged, and it is actually working really well.

But I think that for new people, --use-on-cd should use the recursive strategy by default, because I assume that it is the expected behavior to go back to default when leaving the directory. Maybe it could induce a breaking change though.

In any case, mentioning it in the documentation would be quite helpful for newcomers I think.

Thanks to that feature, I can finally ditch nvm and get back 500ms of startup time on my shell, so thanks for the great work!

[taylorkline]

@Schniz Would a PR to update the README.md to mention that the --version-file-strategy=recursive flag may be desired with the --use-on-cd addition to the shell configs?