[draft] Doc: add document watermarking section

Add section "Eliminating Tracking Dots in Printed Documents":

548116ee - add document watermarking section d50e7c87 - warning: physical copies of digital material

cf. Forensic Analysis and Anonymisation of Printed Documents

...While the characteristics and information content of these patterns is chiefly unknown, we describe our analysis of these patterns in the following for reusability. Additionally we explore anonymisation approaches against this extrinsic signature to defeat arbitrary tracking. Finally we present our toolkit which implements the entire workflow of extracting,..

This [draft] section clarifies what tracking pixels in printed documents are capable of, how they are used in forensic investigations, as well as how to defeat them using the toolkit Deda. Deda is able to remove tracking from printed documents, which can be used to find the exact model number and serial number, as well as, in some extreme cases, reveal the location of the printer.

Closes #191 (closed)