Current output from "jlink --list-plugins" has:

Plugin Name: copy-files
Option: --copy-files=<List of <file path>=<image target> to copy to the image>.
Description: If files to copy are not absolute path, JDK home dir is used.
e.g.: jrt-fs.jar,LICENSE,/home/me/myfile.txt=somewehere/conf.txt

"somewehere" should be "somewhere"