update the man-page with fresh examples

doc/prt-get.8

@@ -777,6 +777,13 @@ reasonably up-to-date system, the two processes in the above command will
 return many identical lines; these are suppressed by the -3 flag to
 \fBcomm(1)\fP.
 
+.TP
+.B for L in /var/log/pkgmk/*.log; do P=${L%.log}; P=${P##*/}; prt\-get isinst $P >/dev/null || rm $L; done
+(based on a feature request by samsep10l) a command you can put into root's
+crontab in order to mimic Slackware's tidy directory listings (logs are only
+kept for the packages that are actually installed). Modify as needed depending
+on the format string and the log directory specified in \fBprt\-get.conf(5)\fP.
+
 .TP
 .B prt\-get printf \(dq%p\et%u\en\(dq | awk '($1 ~ /\e/myrepo$/) { print $2 }'
 Print the upstream URL for each port in the collection \(dqmyrepo\(dq, perhaps