diff --git a/addinfo.sh b/addinfo.sh
index b28c952..baa1d29 100644
--- a/addinfo.sh
+++ b/addinfo.sh
@@ -32,6 +32,11 @@ set -e
 # uncompress snapshot.complete.idx.xz to both snapshot.complete.idx and
 # snapshot.idx, and then run "sh addinfo.sh -c YYYYMMDD" with the oldest
 # known snapshot.
+#
+# $ xzcat snapshot.idx.xz  | awk '{ print $5 }' | sort -u
+# $ unxz < snapshot.complete.idx.xz > snapshot.complete.idx
+# $ unxz < snapshot.complete.idx.xz > snapshot.idx
+
 
 SNAPDIR=$(dirname $0)
 MAILDIR="$SNAPDIR"/mail