docs: clarify custom route path usage with `localePath` and `<NuxtLinkLocale>`

[MickL]

🔗 Linked issue

https://github.com/nuxt-modules/i18n/issues/2767

❓ Type of change

• [X] 📖 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

It wasnt documented that can use named routes.

📝 Checklist

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