feat: document non top level partials

[alestiago]

Status

READY

Description

Today I forgot that I raised https://github.com/felangel/mason/issues/378, when looking at the documentation there was no reminder/information about it, and I think it is worth mentioning it within the documentation.

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [X] 📝 Documentation
• [ ] 🗑️ Chore

[alestiago]

Closed for #1355, I based on main during development but mason uses master and the history was all over the place.