/usr/share/doc/libhighgui-dev/README.Debian is in libhighgui-dev 2.3.1-7.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libhighgui-dev/../libopencv-highgui-dev/README.Debian
/usr/share/doc/libhighgui-dev/../libopencv-highgui-dev/README.Debian