/usr/share/doc/libshibsp-plugins/README.txt is in libshibsp-plugins 2.6.1+dfsg1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libshibsp-plugins/../libshibsp7/README.txt
/usr/share/doc/libshibsp-plugins/../libshibsp7/README.txt