Fix docs for rain total in [[sensor_map]] ?

[sandeen]

Hi Matthew -

I think that upstream weewx might need rainTotal rather than rain_total for the sensor map examples:

    [[sensor_map]]
        windDir = wind_dir.0BFA.Acurite5n1Packet
        windSpeed = wind_speed.0BFA.Acurite5n1Packet
        outTemp = temperature.0BFA.Acurite5n1Packet
        outHumidity = humidity.0BFA.Acurite5n1Packet
        rain_total = rain_total.0BFA.Acurite5n1Packet
        inTemp = temperature.24A4.AcuriteTowerPacket
        inHumidity = humidity.24A4.AcuriteTowerPacket

Not sure if this is a recent change, but i wasn't getting rain reported Weather Underground until I made that change.
I couldn't tell how to find what all the expected weewx names are, though ...?

[sandeen]

Ok now I'm not sure about this, but still not sure how to find the definitive list of database names ...