add custom_types ref

data/1.rust初阶/2.rust基本概念/3.可自定义类型/custom_types.md

@@ -162,7 +162,7 @@ fn main() {
 
 ```
 
-###
+### 使用 Tuple stype Struct
 
 ```rust
 
@@ -199,3 +199,7 @@ fn main() {
 }
 
 ```
+
+<!-- ref:
+https://doc.rust-lang.org/rust-by-example/custom_types/structs.html
+https://stevedonovan.github.io/rustifications/2018/08/18/rust-closures-are-hard.html -->
\ No newline at end of file