Update README for xnat_configuration

[AnilMistry]

The current version requires a verify = True/False flag, but this isnt reflected in the readme.

    xnat_configuration = {'server': "http://localhost",
                          'user': "admin",
                          'password': "admin",
                          'project': "XXXX",
                          'verify': True
                          }

[laurencejackson]

Thanks for flagging @AnilMistry. You're correct, this is required for the live version of XNAT in our case. I will tidy up the way that variable is used so it doesn't cause this issue, and will update the documentation accordingly