Update help message to specify unit of --segment-size option.
Update help message to specify unit of --segment-size option.

Change-Id: Ic3f9a733329c19c4e0bb85676da28a8d1d74232b
Closes-Bug: 1302566

sohonetlabs/python-swiftclient,VyacheslavHashov/python-swiftclient,jeseem/python-swiftclient,zackmdavis/python-swiftclient,iostackproject/IO-Bandwidth-Differentiation-Client,zackmdavis/python-swiftclient,varunarya10/python-swiftclient,openstack/python-swiftclient,krnflake/python-hubicclient,pratikmallya/python-swiftclient,iostackproject/IO-Bandwidth-Differentiation-Client,openstack/python-swiftclient,ironsmile/python-swiftclient,JioCloud/python-swiftclient,VyacheslavHashov/python-swiftclient,jeseem/python-swiftclient,ironsmile/python-swiftclient,sohonetlabs/python-swiftclient,JioCloud/python-swiftclient,varunarya10/python-swiftclient,pratikmallya/python-swiftclient