docs: add lang switching vue-i18n caveat

[BobbieGoede]

🔗 Linked issue

❓ 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

This is a common pitfall and I'm guessing this mostly happens for users who first used vue-i18n only. Directly mutating locale and not using setLocale or switchLocalePath navigation when switching language is an easy mistake, hopefully this informs users before they make it or at least it can be referenced when users open an issue.

I'm thinking we should probably add a section with common pitfalls or best practices that includes bits of information like this.

📝 Checklist

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

[nuxt-studio[bot]]

✅ Live Preview ready!

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