/usr/share/doc/libgtkmm-3.0-dbg/README is in libgtkmm-3.0-dbg 3.18.0-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtkmm-3.0-dbg/../libgtkmm-3.0-1v5/README
/usr/share/doc/libgtkmm-3.0-dbg/../libgtkmm-3.0-1v5/README