Sylvia/docs/ora 65

@mhoeber @lamagnifica @stephensanchez @wedaly @gradyward Please review. This is a draft so things may be a little rough around the edges, and I have a couple of notes to myself inline.
It might be helpful to provide a brief intro that iterates through the components of an open responses assessment. ("You build a __ by..." kind of thing.) An alternative would be to add a transitional sentence from one step to the next. ("Next, you add the question that students will see when they view the problem" etc.)