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.
For the new event exports you only have to decrypt the files. The files can be processed while compressed, or they can be decompressed if required.

For the database export the process is the one described here, where the files are unpacked and then have to decrypted. They get decompressed by the same process that decrypts them (which is different from the event files).