update docs

mybatis-flex-core/src/test/java/com/mybatisflex/test/AccountSqlTester.java

@@ -160,6 +160,18 @@ public class AccountSqlTester {
         System.out.println(sql);
     }
 
+    @Test
+    public void testOrderBySql() {
+        QueryWrapper queryWrapper = QueryWrapper.create()
+                .select()
+                .from(ACCOUNT)
+                .orderBy(ACCOUNT.AGE.asc(),ACCOUNT.USER_NAME.desc().nullsLast());
+
+        IDialect dialect = new CommonsDialectImpl();
+        String sql = dialect.forSelectListByQuery(queryWrapper);
+        System.out.println(sql);
+    }
+
     @Test
     public void testDeleteSql() {
         IDialect dialect = new CommonsDialectImpl();

readme_zh.md

@@ -253,6 +253,19 @@ QueryWrapper queryWrapper=QueryWrapper.create()
 // HAVING age BETWEEN  ? AND ?
 ```
 
+### orderBy
+
+```java
+QueryWrapper queryWrapper=QueryWrapper.create()
+        .select()
+        .from(ACCOUNT)
+        .orderBy(ACCOUNT.AGE.asc(), ACCOUNT.USER_NAME.desc().nullsLast());
+
+// SQL: 
+// SELECT * FROM `tb_account` 
+// ORDER BY `age` ASC, `user_name` DESC NULLS LAST
+```
+
 ### join
 
 ```java