Encourage instructors to get a SEPARATE license in the interface

[novoselt]

Reasons:

• it is nice for instructors to have more powerful licenses, in particular regarding disk space and timeout
• if instructor hits any limits and needs to upgrade the license, it is WAY easier to accomplish with a separate license

The docs do have (gentle) encouragement to do so: https://doc.cocalc.com/teaching-upgrade-course.html#apply-the-course-license-to-the-instructor-project-optional But since people don't read the docs, especially every time they create a course, if would be nice to have an in-your-face reminder.