modify upload text for different data types

[wholmgren]

The dashboard forecast upload example is this:

# optional header, ignored by Solar Forecast Arbiter 
timestamp,value
2018-11-22T12:00:00Z,10.23
2018-11-22T12:05:00Z,10.67

Those values only make sense for deterministic forecasts and forecasts for percentiles. Event forecasts should be 0 or 1. I don't remember the convention for probabilities (0-1 or 0-100%) but maybe those need to change too.

The same should be done for uploads of observations for events.