Update iana-enum-template.txt

Author: boucadair

templates/iana-enum-template.txt

@@ -31,7 +31,7 @@ and sub-statements thereof, should be defined:
 Unassigned or reserved values are not present in the module.
 
 When the "iana-foo" YANG module is updated, a new "revision"
-statement with a unique revision date must be added in front of the
+statement with a unique revision date needs to be added in front of the
 existing revision statements. The "revision" statement MUST contain 
 both "description" and "reference" substatements as follows.