Document the coordinate system

[pentamassiv]

Is your feature request related to a problem? Please describe.
The coordinate systems are different for the various platforms. Enigo reverts them on some of the platforms. This might be confusing to the user. We mention the origin of the coordinate system in the docs, but a picture might be nice to have, similar to:

(Copied from https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CocoaDrawingGuide/Transforms/Transforms.html)