PUBDEV-4833: Documentation updates for PySparkling Install (#1479)
PUBDEV-4833: Documentation updates for PySparkling Install (#1479)

Updated the installation instructions for PySparkling based on the info
from the download site.
h2oai/h2o-3,mathemage/h2o-3,mathemage/h2o-3,h2oai/h2o-dev,h2oai/h2o-dev,michalkurka/h2o-3,spennihana/h2o-3,michalkurka/h2o-3,h2oai/h2o-dev,michalkurka/h2o-3,h2oai/h2o-3,spennihana/h2o-3,mathemage/h2o-3,h2oai/h2o-dev,mathemage/h2o-3,h2oai/h2o-dev,h2oai/h2o-3,spennihana/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-dev,h2oai/h2o-3,spennihana/h2o-3,michalkurka/h2o-3,mathemage/h2o-3,mathemage/h2o-3,michalkurka/h2o-3,michalkurka/h2o-3,michalkurka/h2o-3,spennihana/h2o-3,h2oai/h2o-dev,mathemage/h2o-3,spennihana/h2o-3,spennihana/h2o-3,h2oai/h2o-3,h2oai/h2o-3