conf/create_opendkim_key.conf.sample: add parameter 'dns_main_zone_master_server'. Only relevant if the underlying zone is not yet registered.

conf/create_opendkim_key.conf.sample

@@ -7,6 +7,15 @@
 # DNS Server
 # ----------
 
+# - dns_main_zone_master_server
+# -
+# - if main zone (for which a DKIM key should be created) isn't already registered, then 
+# - try this nameserver.
+# -
+# - This requires that the name servers are already set up.
+# -
+#dns_main_zone_master_server=
+ 
 # - dns_dkim_zone_master_server
 # - 
 # - The DNS Server who is serving the update zone and is used