Document how to hand off/pick up an interview project

[samglover]

In the LIT Clinic, interview projects are often started by one student or team of students, who take it through one phase over the course of a semester, then set it aside. Then another student or team of students will pick up the interview project and takes it through the next phase.

In other cases, an interview may need to be updated after it has been live for months or years, and the person or team responsible for updating it is not the same that built it in the first place.

See #460 and #460 for related issues.