docs: add MCP server docs

[reidbarber]

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the documentation
• View the S2 docs

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the documentation
• View the S2 docs

[snowystinger]

I know these are probably their styles, but they look so much like status badges letting you know if a github repo is passing tests. Probably why they are called badge.

[snowystinger]

Also, syntax highlight is a little off

[reidbarber]

Also, syntax highlight is a little off

Ahh yeah I used js as the language since we don't support toml and providing no language doesn't work well with multiline example. We can probably improve this later.