docs: add populate nested field docs

[jiblett1000]

Types of changes

• [ ] Bug fix (a non-breaking change which fixes an issue)
• [ ] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

This PR adds a little snippet under the find() docs describing how to populate nested fields which isn't readily apparent. It took me (and at least one other person) many hours of searching around and exhausting every option before finally sorting this out. I'm not sure if this is the best place for it, but I feel based on the lack of documentation elsewhere on using the dot notation here, it should be added somewhere at least.

Checklist:

• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes (if not applicable, please state why)