docs: add auto-translate workflow guide

[sidemt]

Checklist:

• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)

This is a guide for the i18n team about the new auto-translation GitHub Actions workflow.

[sidemt]

Thanks for your feedback, @ilenia-magoni and @ojeytonwilliams !

[ojeytonwilliams]

Thanks, Yoko. I'm not in a position to judge if these are correct, so I won't leave an approval, but I do think the language is clear!