Draft for DOC-392

@mhoeber and @srpearce , would you give me opinions on tone, structure,
and level of detail? Just the first section for course teams is
complete, but I'm not entirely satisfied with the track I'm on right
now.
I don't think I'd start with "Course teams, researchers, developers, students: the edX community..." - it feels a bit like "Space: The final frontier" to me. I also think "and uses a number of delivery formats" is kind of redundant. Working on a suggestion now...