/usr/share/doc/libmsgpack-dev/README is in libmsgpack-dev 0.5.7-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmsgpack-dev/../libmsgpack3/README
/usr/share/doc/libmsgpack-dev/../libmsgpack3/README