[2041] SQLite_ubench journal_mode is now described.

tests/tools/dhcp-ubench/README

@@ -127,6 +127,11 @@ To improve performance, asynchronous mode is used (PRAGMA synchronous = OFF).
 If you do not like it, modify SQLite_uBenchmark::connect() by commenting it out
 and suffer the pain of having around 10 inserts per seconds.
 
+Another tweakable feature is journal mode. It can be turned to several modes
+of operation. Its value can be modified in SQLite_uBenchmark::connect().
+See http://www.sqlite.org/pragma.html#pragma_journal_mode for detailed
+explanantion.
+
  Performance optimizations
 ---------------------------