Completing the information of insert into select clause in direct-mode

src/sql/optimizer/ob_explain_note.h

@@ -31,6 +31,7 @@ namespace sql
 #define PARALLEL_ENABLED_BY_SESSION "Degree of Parallelism is %ld because of session"
 #define PARALLEL_ENABLED_BY_TABLE_PROPERTY "Degree of Parallelisim is %ld because of table property"
 #define PARALLEL_DISABLED_BY_PL_UDF_DAS  "Degree of Parallelisim is %ld because stmt contain pl_udf which force das scan"
+#define DIRECT_MODE_INSERT_INTO_SELECT  "Direct-mode is enabled in insert into select"
 
 }
 }