Clarify resulting location of files from download command

[kozbo]

As an end user of the hca dss download command I would like to know where the files will end up.

The help says that the file will be downloaded to a local directory, and the INFO messages show where the file is being loaded into the filestore. Users will get confused by this.

Suggestions:

1. expand on the help text to add that the files from the bundle will be put in a local directory named after the UUID of the bundle.
2. Demote the INFO messages that describe were the files are being put to be DEBUG level messages instead

@jessebrennan

[theathorn]

Create readme file after download.