benchmark: clarify some expressions in sysbench report (pingcap#3558)

* benchmark: clarify some expressions in sysbench report

Signed-off-by: Ran <huangran@pingcap.com>

* Update benchmark/benchmark-tidb-using-sysbench.md

Co-authored-by: TomShawn <41534398+TomShawn@users.noreply.github.com>

benchmark/benchmark-tidb-using-sysbench.md

@@ -59,7 +59,7 @@ enabled = true
 
 Higher log level also means better performance for TiKV.
 
-There are 2 Column Families (Default CF and Write CF) on TiKV cluster which are mainly used to store different types of data. For the Sysbench test, the Column Family that is used to import data has a constant proportion among TiDB clusters:
+There are multiple Column Families on TiKV cluster which are mainly used to store different types of data, including Default CF, Write CF, and Lock CF. For the Sysbench test, you only need to focus on Default CF and Write CF. The Column Family that is used to import data has a constant proportion among TiDB clusters:
 
 Default CF : Write CF = 4 : 1