[docs] Citing original sources of test documentation

Hey Tobie & all,

As I/we are migrating & updating documentation from many sources, should we follow a process to credit or cite those sources?

A few options:

 1.  Link to archived and clearly deprecated previous version (assuming everything stays alive somewhere)
 2.  Names of the original authors
 3.  Generic citation:  "Sourced and updated from w3.org or http://wiki.csswg.org/test"
 4.  No citation

Thoughts?

-Rebecca