Submission Editors setting help text update

[ajrbyers]

Is your feature request related to a problem? Please describe.
Sometimes when looking at the Editors notified on submission setting it’s not clear why a certain editor received an email.

Describe the solution you'd like
There are two options:

1. update the setting description to explain that who receives notifications can be overwritten at the section level
2. add a combined interface for notification submissions including fallback and section level