docs(modal): mention how to programatically close

[sdezza]

🔗 Linked issue

https://ui.nuxt.com/components/modal#control-programmatically

❓ 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

May sounds easy but mentioning how to close the modal using the new "Control programmatically" method can be susefull.

📝 Checklist

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