Add Netlify _redirects file

This ensures the URLs can be navigated to directly.

Tested in #146

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Commit:  ember-learn/super-rentals-tutorial@ba546ad
Script:  https://github.com/ember-learn/super-rentals-tutorial/blob/ba546ade32f43c118706d878a8b8250191ccf4bb/.github/workflows/build.yml
Logs:    https://github.com/ember-learn/super-rentals-tutorial/commit/ba546ade32f43c118706d878a8b8250191ccf4bb/checks