Fathead: Document how much data processing is done behind the scenes

[jagtalon]

I think it's worth documenting how we process the output.txt behind the scenes. For example, it's hard to tell if:

• Do the keys need to be lowercased?
• Do I need to add multiple keys for Date.parse() such as Date.parse, Date parse, and Date parse()?
• Do we need to add the triggers in the keys such as jquery each instead of just each?

CC @jdorweiler