Small fix to description of container GET.

The text said that you'd get a 2xx response if the container was
empty, but didn't say anything about when the container was
nonempty. Well, you get a 2xx whether the container is empty or not,
so now the text reflects that.

Thanks to Clay Gerrard for spotting this.

Change-Id: Ib0a37d6a3689834fa799ffe51988add3453fb746