add one exercise in patterns.md

solutions/pattern-match/patterns.md

@@ -85,4 +85,17 @@ fn main() {
         }
     }
 }
+```
+
+6.
+```rust
+fn main() {
+    let mut v = String::from("hello,");
+    let r = &mut v;
+
+    match r {
+        // The type of value is &mut String
+       value => value.push_str(" world!") 
+    }
+}
 ```

src/pattern-match/patterns.md

@@ -101,4 +101,19 @@ fn main() {
 }
 ```
 
+6. 🌟🌟 Using pattern `&mut V` to match a mutable reference needs you to be very careful due to `V` being a value  after matching
+```rust,editable
+
+// FIX the error with least changing
+// DON'T remove any code line
+fn main() {
+    let mut v = String::from("hello,");
+    let r = &mut v;
+
+    match r {
+       &mut value => value.push_str(" world!") 
+    }
+}
+````
+
 > You can find the solutions [here](https://github.com/sunface/rust-by-practice)(under the solutions path), but only use it when you need it

zh-CN/src/pattern-match/patterns.md

@@ -97,4 +97,19 @@ fn main() {
 }
 ```
 
+6. 🌟🌟 使用模式 `&mut V` 去匹配一个可变引用时，你需要格外小心，因为匹配出来的 `V` 是一个值，而不是可变引用
+```rust,editable
+
+// 修复错误，尽量少地修改代码
+// 不要移除任何代码行
+fn main() {
+    let mut v = String::from("hello,");
+    let r = &mut v;
+
+    match r {
+       &mut value => value.push_str(" world!") 
+    }
+}
+````
+
 > 你可以在[这里](https://github.com/sunface/rust-by-practice)找到答案(在 solutions 路径下)