/usr/lib/libRSSKit.so is in librsskit-dev 0.4-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/GNUstep/Frameworks/RSSKit.framework/Versions/Current/libRSSKit.so
/usr/lib/GNUstep/Frameworks/RSSKit.framework/Versions/Current/libRSSKit.so