Document plugin structure for public models

[ucancallmealicia]

The plugin structure for public models is not fully documented. Specifically, it is unclear that to override a model it is only necessary to include the method that is being overridden, not the entire file, and that it is also necessary to name the override file something different than the original file name.

[Blake-]

@ucancallmealicia
Thanks for this idea! The tech-docs committee will work on getting a better description for the plugin structure in place!