#21 Doc Issue -keywords

[Andreas Kupries]

Given that img2pdf -keywords a b c translates this to a,b,c in the generated PDF, and
that pdf4tcl simply passes the value of metadata -keywords into the PDF as is (x) I believe that it should be either

1. documented that multiple keyword values should be entered as comma-separated string, or

2. the code modified to perform the necessary [join $value ,] for metadata(Keywords) and then the value of -keywords documented to be a Tcl list.