restore: add faq for rule not found (#16091)

faq/backup-and-restore-faq.md

@@ -296,6 +296,10 @@ Note that even if you configures [table filter](/table-filter.md#syntax), **BR d
 - System variable tables (`mysql.tidb`, `mysql.global_variables`)
 - [Other system tables](https://github.com/pingcap/tidb/blob/master/br/pkg/restore/systable_restore.go#L31)
 
+### How to deal with the error of `cannot find rewrite rule` during restoration?
+
+Examine whether there are tables in the restoration cluster sharing the same name as other tables in the backup data but having inconsistent structures. In most cases, this issue is caused by missing indexes in the tables of the restoration cluster. A recommended approach is to delete such tables in the restoration cluster first and then retry restoration.
+
 ## Other things you may want to know about backup and restore
 
 ### What is the size of the backup data? Are there replicas of the backup?