Add under environment section for lightning strike detectors

[mgrouch]

#610

[tkurki]

It is unclear to me how the fields suggested should be used. For example totalDetected and and detectionPeriod appear to be about summary data about a period, but they are handled separately as separate numberValues that have source and timestamp data.

If you want to pursue this further it would be useful to start from deltas: what kind of deltas would a source for this type of data send out? Then we can figure out what kind of additions to the spec this warrants.

I have to add that I feel I am out of my depth such stuff, without consulting some real world lightning data sources.

Feel free to reopen if you want to discuss this further, but I think this needs a fresh start.