Cleanup: correct cli --volumes-from description

issue #7580 volumes-from comma separated list mentioned this case.

Options like --volumes-from=[] indicate they can be specified multiple times:
docker run -it --rm --volumes-from TEST_DATA --volumes-from TEST_DATA2 ubuntu bash

Signed-off-by: Deshi Xiao <dxiao@redhat.com>
Merge pull request #7640 from xiaods/develop

Cleanup: correct cli --volumes-from description