The user guide shows that options passed to connection.from_config do
not have to be an argparse Namespace, contrary to the comments in
connection.from_config. This change corrects those comments and adds
a user guide example showing how argparse may be used.
Change-Id: I2a9e92cbf0aab16476001be772034e9698a24c9f
Closes-Bug: #1629331
6f2209e238