Ahodges/documentation/for662

Added procedures for adding posts, responses, and comments in discussion topics on the Discussion page and in the courseware. Also added contextual information ("Anatomy") for students.
This last sentence is a bit unwieldy. Maybe: Before you add a post, response, or comment, we recommend that you take a moment to consider which of these options best suits the contribution you want to make. This will help keep the discussion organized and easy to follow.