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.
Either "supply a video start time or a video stop time" or "Supply values in the **Video Start Time** or **Video Stop Time** fields"