cherry pick pingcap#4516 to release-5.0

Signed-off-by: ti-srebot <[email protected]>

tiflash/use-tiflash.md

@@ -53,7 +53,9 @@ ALTER TABLE `tpch50`.`lineitem` SET TIFLASH REPLICA 0
     CREATE TABLE table_name like t
     ```
 
-* For the current version, if you create the TiFlash replica before using TiDB Lightning to import the data, the data import will fail. You must import data to the table before creating the TiFlash replica for the table.
+* For versions earlier than v4.0.6, if you create the TiFlash replica before using TiDB Lightning to import the data, the data import will fail. You must import data to the table before creating the TiFlash replica for the table.
+
+* If TiDB and TiDB Lightning are both v4.0.6 or later, no matter a table has TiFlash replica(s) or not, you can import data to that table using TiDB Lightning. Note that this might slow the TiDB Lightning procedure, which depends on the NIC bandwidth on the lightning host, the CPU and disk load of the TiFlash node, and the number of TiFlash replicas.
 
 * It is recommended that you do not replicate more than 1,000 tables because this lowers the PD scheduling performance. This limit will be removed in later versions.