added description of plutostderrlog parameter to ipsec.conf.5 man page

src/starter/ipsec.conf.5

@@ -1061,6 +1061,10 @@ so running interactive commands is difficult unless they use
 or equivalent for their interaction.
 Default is none.
 .TP
+.B plutostderrlog
+Pluto will not use syslog, but rather log to stderr, and redirect stderr
+to the argument file.
+.TP
 .B virtual_private
 defines private networks using a wildcard notation.
 .PP