Sylvia/docs/sfd discussions

@mhoeber @lamagnifica @catong This is finally ready for review. I accidentally added some extra images, so please ignore the ones that don't apply (I'll take them out before I merge this). I tried to create a built version but RTD inexplicably created the course staff release notes page (grr); will try again tomorrow.

Update: RTD is working! See http://draft-sfd-discussions.readthedocs.org/en/latest/.
consider breaking this into two images, one with 5 callouts on left and one with 3 on right, and inserting at two different points in the text? seeing 8 different things in red and lines and circles all at once is a bit overwhelming (and I know what I'm looking at...)
It also saddens me to see this move away from a task-oriented organization, where a user had particular goals to accomplish and could look for info on how to do any one of them, and instead conform the information to match how the UI presents them.