Ahodges/documentation/doc764

@WatsonEmily , please distribute for PM review for usability by our audience.
@jhelbert , @stroilova , @shnayder , @rocha  please review for accuracy, completeness, and level of detail, particularly wrt data czars who will need to revise scripts for post-download processing.
@mhoeber , @srpearce please copy edit.
No. There is two websites, edx.org and edge.edx.org. Each one has a prod (production) and a stage environment, for combinations in total: edx/prod, edge/prod, edx/stage and edge/stage. Sometimes people refer to edx/prod as just prod, but it is not clear enough. We don't export data from the stage environments, only production (edx/prod, edge/prod).