Mention associations in Form Helpers guide [ci-skip]
Mention associations in Form Helpers guide [ci-skip]

This fleshes out the "Choices from a Collection of Complex Objects"
section a bit more, explicitly mentioning associations and proper field
naming.

BlakeWilliams/rails,rails/rails,esparta/rails,MSP-Greg/rails,georgeclaghorn/rails,rails/rails,yahonda/rails,georgeclaghorn/rails,BlakeWilliams/rails,rails/rails,rails/rails,georgeclaghorn/rails,BlakeWilliams/rails,MSP-Greg/rails,MSP-Greg/rails,yahonda/rails,MSP-Greg/rails,esparta/rails,georgeclaghorn/rails,esparta/rails,yahonda/rails,esparta/rails,BlakeWilliams/rails,yahonda/rails