Documentation: Add processing info graphic

[Herdo]

Given the following graphic:

It would be nice to know more about the "black magic" in the middle.

• Where are my *.csx files coming in?
• What is "injected" (as globals) into those files?
• If not via the "Run Custom Tool" trigger, what's creating my list of files
• etc.

The explanation should be in a graphic, displaying the different steps being executed - from the trigger (grey box) to the final file (green file).