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.
Can we add two notes at the end of 4.2:
 
NOTE: By adding the edX ID, you associate your video component with the following elements: YouTube, AWS, and mobile. Therefore, you do not need to add a separate element for YouTube or download links in Studio. By adding the edX ID, these steps are complete. 

NOTE: Adding the edX ID is separate from adding transcripts for your files. You still need to add transcripts for your videos in Studio.