add docstr to v2 shell module regarding CLI deprecation
add docstr to v2 shell module regarding CLI deprecation

Change-Id: Iaafd00671c634ab64352c5cfab0470dae0b53c35

darren-wang/ksc,ging/python-keystoneclient,darren-wang/ksc,sdpp/python-keystoneclient,klmitch/python-keystoneclient,ging/python-keystoneclient,magic0704/python-keystoneclient,klmitch/python-keystoneclient,alexpilotti/python-keystoneclient,Mercador/python-keystoneclient,Mercador/python-keystoneclient,sdpp/python-keystoneclient,alexpilotti/python-keystoneclient,jamielennox/python-keystoneclient,jamielennox/python-keystoneclient,magic0704/python-keystoneclient,jamielennox/python-keystoneclient