WIP: Documentation for Publishing Changes

Some of the text in this section feels a bit redundant, and I'd change "never" in the first sentence to "cannot" - "never" implies that even if the release date passes, students won't be able to see the section. 

Maybe:

Students cannot see any content in the section if the section's release date is unscheduled or has not passed.

If a section's release date has passed, students can see content in the section if:

- The release date for the subsection that contains that content has passed.
- The unit has been published.
- The unit is not hidden from students.