Add validation rules docs

[flozdra]

🔗 Linked pull request

adonisjs/lucid#1012

❓ Type of change

• 🐞 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

I've added the documentation about the validation rules added by Lucid to VineJS.
However, this is not the final version as modifications may be applied to the options parameters in the PR. ⚠️
Tell me if you want to add or modify something.

📝 Checklist

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