Fix readme: MaxIdle is same or less than MaxOpen (#1215)

Co-authored-by: wanglonghui7 <wanglonghui7@jd.com>

Author: lowang-bh

README.md

@@ -85,7 +85,7 @@ db.SetMaxIdleConns(10)
 
 `db.SetMaxOpenConns()` is highly recommended to limit the number of connection used by the application. There is no recommended limit number because it depends on application and MySQL server.
 
-`db.SetMaxIdleConns()` is recommended to be set same to (or greater than) `db.SetMaxOpenConns()`. When it is smaller than `SetMaxOpenConns()`, connections can be opened and closed very frequently than you expect. Idle connections can be closed by the `db.SetConnMaxLifetime()`. If you want to close idle connections more rapidly, you can use `db.SetConnMaxIdleTime()` since Go 1.15.
+`db.SetMaxIdleConns()` is recommended to be set same to `db.SetMaxOpenConns()`. When it is smaller than `SetMaxOpenConns()`, connections can be opened and closed very frequently than you expect. Idle connections can be closed by the `db.SetConnMaxLifetime()`. If you want to close idle connections more rapidly, you can use `db.SetConnMaxIdleTime()` since Go 1.15.
 
 
 ### DSN (Data Source Name)