/usr/share/help/cs/gnome-system-monitor/fs-diskusage.page is in gnome-system-monitor 3.18.2-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/help/cs/gnome-system-monitor/../../../help-langpack/cs/gnome-system-monitor/fs-diskusage.page