faq: add multistatement faq (pingcap#4029)

Author: Null not nil

faq/tidb-faq.md

@@ -140,6 +140,16 @@ update mysql.tidb set variable_value='30m' where variable_name='tikv_gc_life_tim
 
 Check whether `tidb_disable_txn_auto_retry` is set to `on`. If so, set it to `off`; if it is already `off`, increase the value of `tidb_retry_limit` until the error no longer occurs.
 
+#### ERROR 1105 (HY000): client has multi-statement capability disabled
+
+This error might occur after upgrading from an earlier version of TiDB. To prevent against SQL injection attacks, TiDB now prevents multiple queries being executed in the same `COM_QUERY` call by default.
+
+Check the documentation for your client driver for instructions on how to enable multiple statements. i.e:
+
+* [go-sql-driver](https://github.com/go-sql-driver/mysql#multistatements) (`multiStatements`)
+* [Connector/J](https://dev.mysql.com/doc/connector-j/8.0/en/connector-j-reference-configuration-properties.html) (`allowMultiQueries`)
+* PHP [mysqli](https://dev.mysql.com/doc/apis-php/en/apis-php-mysqli.quickstart.multiple-statement.html) (`mysqli_multi_query`)
+
 ### MySQL native error messages
 
 #### ERROR 2013 (HY000): Lost connection to MySQL server during query