doc/md: fix multi driver missing method (#3390)

doc/md/faq.md

@@ -763,6 +763,10 @@ func (d *multiDriver) Close() error {
 	}
 	return nil
 }
+
+func (d *multiDriver) Dialect() string {
+	return d.r.Dialect()
+}
 ```
 
 #### How to change the character set and/or collation of a MySQL table?
@@ -862,4 +866,4 @@ func (e *EncodeExtension) Hooks() []gen.Hook {
 		},
 	}
 }
-```
+```