Add edX video ID section

Added the video_course.rst file to describe what course teams do after automated processing is complete.
@nasthagiri, @frrrances, @WatsonEmily , @lou-wang, @srpearce 
@mhoeber, @catong FYI.
They can use either method, Upload a New Transcript (which is what our 3Play-using members, like Harvard, will use) or Import YouTube Transcript. Overall, this initial draft is hard to follow. Separately, I sent Alison a revised draft that breaks the options into smaller sections to simplify the instructions.