feat: initiate Korean i18n effort

[wonhyeongseo]

Part of #370

Hello @simoninithomas ,

This PR marks the beginning of our effort to internationalize the Reinforcement Learning Course by adding Korean translations. The main goal of this initiative is to make our course more accessible to Korean-speaking users and expand our reach.

Here are the key changes included in this PR:

1. Created units/ko directory: This new directory will contain all our Korean translations. For this PR, it currently holds _toctree.yml with contents pointing towards the English version.

2. Added ko the language list of build_documentation.yml and build_pr_documentation.yml to enable views.

If you have any suggestions for improvements or spot any errors, please don't hesitate to point them out. Also, for anyone interested in contributing to this Korean i18n effort, your help would be much appreciated.

Looking forward to your feedback.

Best,
Won

[simoninithomas]

Hey there👋 thanks for your work. As mentionned in Discord we don't support other languages for this course for now contrary to the transformer course.

However, what we can do is I can create a moon-ci-docs.huggingface.co link that will allow you to share to people who want to follow the course in Korean (and also see what the course looks like).

Currently there's an error in the Build PR documentation so I can't provide you this link (check the Failing error, from what I see is because you don't have a table of contents

Have a nice day 🤗