Thank you - I have found the readme and it says
Run ${INSTALL_PREFIX}/rss-glx_install.pl, which will look at your existing
~/.xscreensaver and add any missing entries. You probably want to back that
file up as the script is only lightly tested
${INSTALL_PREFIX} is usually /usr/local/bin or /usr/lib/xscreensaver.
but I haven't got either of the paths
is there like a dir rss*.pl /s command
I remember something about grep!! but that was a long time ago (early 90s!)