reference: make tuple usage examples more meaningful

Author: tshepang

src/doc/reference.md

@@ -3322,10 +3322,13 @@ An example of a tuple type and its use:
 
 ```
 type Pair<'a> = (i32, &'a str);
-let p: Pair<'static> = (10, "hello");
+let p: Pair<'static> = (10, "ten");
 let (a, b) = p;
-assert!(b != "world");
-assert!(p.0 == 10);
+
+assert_eq!(a, 10);
+assert_eq!(b, "ten");
+assert_eq!(p.0, 10);
+assert_eq!(p.1, "ten");
 ```
 
 For historical reasons and convenience, the tuple type with no elements (`()`)