create_opendkim_key.sh: fix several errors.

conf/create_opendkim_key.conf.sample

@@ -24,8 +24,10 @@ dns_server="b.ns.oopen.de"
 # -
 # - Zone containing the DKIM TXT record.
 # -
-# - Example:
-# -    update_zone="dkim.oopen.de"
+# - Defaults to '_domainkey.<dkim_domaini>'
+# -
+# - Note:
+# -    do NOT change/set this option unless you know what you do.
 # -
 #update_zone=""
 
@@ -33,8 +35,10 @@ dns_server="b.ns.oopen.de"
 # -
 # - TTL for the DKIM TXT Record.
 # -
-# - Defaults to "360"
-#TTL=360
+# - Defaults to "" if update_dns=false
+# - Defaults to "43200" if update_dns=true
+#
+#TTL=""
 
 
 # ----------