docs: add iconify icon naming convention

[Barbapapazes]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Hey 👋,

I was trying to use Nuxt UI with a Vite + Vue project, and I noticed that the icon i-simple-icons-github was not working as expected. After some investigation, I found that that the request was https://api.iconify.design/simple.json?icons=icons-github, which is incorrect. The collection name should be simple-icons, not simple.

At first, I thought it was a bug in Nuxt UI, but I discovered that Iconify enforces a specific naming convention for icons. The correct way to reference the GitHub icon is i-simple-icons:github, where simple-icons is the collection name and github is the icon name.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@4307

commit: 6958c28