correct example for ISO 3166-1 alpha-2 code

Author: MarcelOliver

osi_trafficsign.proto

@@ -301,11 +301,13 @@ message TrafficSign
 
             // Specifies the country. See ISO 3166-1, alpha-2 codes
             // https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
-            // e.g. "Germany", "France", "Austria"
+            // e.g. "DE", "FR", "AT
+            //"
             optional string country = 8;
 
             // The year the traffic rules come into force
             // e.g. "2017"
+            //
             optional string country_revision = 9;
 
             // Code identifier according to country code