Mention field punning in the docs for patterns

src/doc/trpl/patterns.md

@@ -196,12 +196,27 @@ struct Point {
 let origin = Point { x: 0, y: 0 };
 
 match origin {
-    Point { x: x, y: y } => println!("({},{})", x, y),
+    Point { x, y } => println!("({},{})", x, y),
 }
 ```
 
 [struct]: structs.html
 
+We can use `:` to give a value a different name.
+
+```rust
+struct Point {
+    x: i32,
+    y: i32,
+}
+
+let origin = Point { x: 0, y: 0 };
+
+match origin {
+    Point { x: x1, y: y1 } => println!("({},{})", x1, y1),
+}
+```
+
 If we only care about some of the values, we don’t have to give them all names:
 
 ```rust
@@ -213,7 +228,7 @@ struct Point {
 let origin = Point { x: 0, y: 0 };
 
 match origin {
-    Point { x: x, .. } => println!("x is {}", x),
+    Point { x, .. } => println!("x is {}", x),
 }
 ```
 
@@ -230,7 +245,7 @@ struct Point {
 let origin = Point { x: 0, y: 0 };
 
 match origin {
-    Point { y: y, .. } => println!("y is {}", y),
+    Point { y, .. } => println!("y is {}", y),
 }
 ```