docs: add import instructions when auto-imports are disabled

[deleteme]

🔗 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 like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This modifies the example Bridge config in the readme to include a line of usage instructions for the imports option.

This imports option might be used by people who want to preserve explicit import statements when upgrading to Nuxt Bridge.

Providing a convenient example of where the Nuxt composables would be imported from (#app), this might help avoid incorrectly assuming that they're available from the @nuxt/bridge package or the #imports alias.

📝 Checklist

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