Update README.md

README.md

@@ -268,3 +268,22 @@ var t10 = db.Updateable<Student>()
  .UpdateColumns(it => new Student() { Name="a",CreateTime=DateTime.Now })
  .Where(it => it.Id == 11).ExecuteCommand();
  ```
+
+ ##  4. Mapping
+Priority level  AS>Add>Attribute
+ ### 4.1 Add
+ ```c
+db.MappingTables.Add()
+db.MappingColumns.Add()
+db.IgnoreColumns.Add()
+ ```
+ ### 4.2 AS
+  ```c
+db.Queryable<T>().As("tableName").ToList();
+ ```
+### 4.3 Attribute
+ ```c
+[SugarColumn(IsIgnore=true)]
+public int TestId { get; set; }
+  ```
+