docs/python-client: Document download of collection and user
docs/python-client: Document download of collection and user

manthey/girder,Kitware/girder,adsorensen/girder,RafaelPalomar/girder,jbeezley/girder,RafaelPalomar/girder,sutartmelson/girder,data-exp-lab/girder,adsorensen/girder,kotfic/girder,adsorensen/girder,manthey/girder,Xarthisius/girder,kotfic/girder,RafaelPalomar/girder,RafaelPalomar/girder,data-exp-lab/girder,kotfic/girder,manthey/girder,data-exp-lab/girder,Xarthisius/girder,sutartmelson/girder,Kitware/girder,Kitware/girder,data-exp-lab/girder,girder/girder,jbeezley/girder,kotfic/girder,kotfic/girder,girder/girder,girder/girder,sutartmelson/girder,sutartmelson/girder,jbeezley/girder,data-exp-lab/girder,RafaelPalomar/girder,Xarthisius/girder,jbeezley/girder,adsorensen/girder,sutartmelson/girder,manthey/girder,Xarthisius/girder,Xarthisius/girder,Kitware/girder,adsorensen/girder,girder/girder