improve doc - define what units maxCompactTime is using

h2/src/docsrc/help/help.csv

@@ -1506,7 +1506,7 @@ All connections are closed, open transactions are rolled back.
 
 SHUTDOWN COMPACT fully compacts the database (re-creating the database may further reduce the database size).
 If the database is closed normally (using SHUTDOWN or by closing all connections), then the database is also compacted,
-but only for at most the time defined by the database setting ""h2.maxCompactTime"" (see there).
+but only for at most the time defined by the database setting ""h2.maxCompactTime"" in milliseconds (see there).
 
 SHUTDOWN IMMEDIATELY closes the database files without any cleanup and without compacting.