KS2008: Documentation: date tagging

Many of the documentation files (such as the mentioned v4l1
documentation) would be vastly improved by a simple two-liner at the very
top, saying "This document was written on yyy (date). It was
checked for accuracy by xxx on yyy."

So if our hypothetical webcam driver author tries to use this document and
sees that it was written in 2004, he at least should do careful checking
if this still describes the state of the art.