Minor updates to the PyART data model notebook
Minor updates to the PyART data model notebook

gamaanderson/2017-AMS-Short-Course-on-Open-Source-Radar-Software,openradar/AMS-Short-Course-on-Open-Source-Radar-Software,jjhelmus/AMS-Short-Course-on-Open-Source-Radar-Software,nguy/2017-AMS-Short-Course-on-Open-Source-Radar-Software,openradar/AMS-Short-Course-on-Open-Source-Radar-Software,jjhelmus/AMS-Short-Course-on-Open-Source-Radar-Software,nguy/2017-AMS-Short-Course-on-Open-Source-Radar-Software,gamaanderson/2017-AMS-Short-Course-on-Open-Source-Radar-Software