doc: update rust.md (jaywcjlove#178)

* doc: match let

* update

docs/rust.md

@@ -853,12 +853,25 @@ let (x, _, y) = (1, 2, 3);
 println!("{x},{y}");
 ```
 
+----
+
+```rust
+fn get_count_item(s: &str) -> (&str, &str) {
+    let mut it = s.split(' ');
+    let (Some(str1),Some(str2)) = (it.next(),it.next()) else {
+        panic!("Can't segment count item pair");
+    };
+    (str1, str2)
+}
+```
+
 ### 函数中的模式匹配
 
 ```rust
 fn add((x, y): (i32, i32)) -> i32 {
     x + y
 }
+
 fn main(){
   let sum = add(1, 2);
   println!("{sum}");