Adding a doc site using Nextra

[ProKil]

Closes #75

This is deployed onto https://docs.sotopia.world!

📑 Description

✅ Checks

• [x] My pull request adheres to the code style of this project
• [x] My code requires changes to the documentation
• [x] I have updated the documentation as required
• [x] All the tests have passed
• [x] Branch name follows type/descript (e.g. feature/add-llm-agents)
• [x] Ready for code review

ℹ Additional Information

[lwaekfjlk]

Looks like https://dev.sotopia.world/ is not reachable?

[ProKil]

sorry my bad. https://docs.sotopia.world

[ProKil]

@lwaekfjlk @XuhuiZhou This PR aims at adding the doc site. Please review and merge and we can work on #76 and #77

[ProKil]

OK I will change the index.mdx

[ProKil]

@lwaekfjlk Check out docs.sotopia.world

[lwaekfjlk]

yes, checked. looks good.