Add additional documentation to VBO BehaviorSessionData page

[matchings]

This page is generally lacking in documentation: https://allenswdb.github.io/physiology/ophys/visual-behavior/VB-BehaviorSessionData.html

For example, what are the metrics in the get_behavior_performance_metrics() table? What are the columns in the trials table?

Most tables are already documented in the VisualBehaviorOphysDataset page, but they should be documented in both places, and there are a few things that are behavior specific that should be emphasized in the behavior page