DOC: Add explanation of empty rest logging defaults

conf/core/server.conf

@@ -112,6 +112,7 @@ GRPC_RESPONSE_LOG_FORMAT={method} {local-address} {remote-address} {user-agent}
 # Logging format of the REST API.
 # Known keys: see column "Variable name" at https://javadocs.restlet.talend.com/2.4/jse/api/index.html?org/restlet/util/Resolver.html
 # 'OFF' turns off the logging.
+# Leaving this empty means using restlet's default settings.
 REST_RESPONSE_LOG_FORMAT=
 
 # --------------------------------------------------