Arvados

When invoked without a file on the command line, arv-put reads from stdin. This can be surprising to new users. It should print a message that it is reading from stdin.

Also, a user wanted to create an empty collection, but you can't do that with arv-put (the way to do this with 'arv' isn't at all obvious, nor properly documented). An option like --empty or --create-empty-collection would avoid confusion.