Description

TaskFlow API tutorial should add an example to use a classic operator (example: EmailOperator) so that users know that it can be leveraged.

Alternatively, it should add references to how to add dependencies (implicit or explicit) to classic operators.

Use case / motivation

It's not super clear how can TaskFlow API be used with existing operators (aka PostgresOperator, EmailOperator...). Adding an example, will facilitate users to get a picture of what can be done with this.