Improve documentation around event window/lead time analysis

[MahmoodEtedadi]

Is your feature request related to a problem? Please describe

The current documentation on event window and lead time analysis lacks clarity and could be enhanced for better understanding.

Describe the solution you'd like

Make it clear how provided params in usage_config related to event window (in particular, window_hr, window_offset and merge_strategy) are used. Including a graph to illustrate the relative placement of the time window and the actual event would be very helpful.