reference: explicit return at function end is not idiomatic

Author: tshepang

src/doc/reference.md

@@ -3504,7 +3504,7 @@ An example of a `fn` type:
 
 ```
 fn add(x: i32, y: i32) -> i32 {
-    return x + y;
+    x + y
 }
 
 let mut x = add(5,7);