Update tuples.md

Small clarification. I don't know if there are more restrictions apart from the size in this case (as I am just learning the language) but this should help clarifying how long does `long` mean.

Author: cdvv7788

src/primitives/tuples.md

@@ -35,7 +35,7 @@ fn main() {
     // Tuples are printable
     println!("tuple of tuples: {:?}", tuple_of_tuples);
     
-    // But long Tuples cannot be printed
+    // But long Tuples (more than 12 elements) cannot be printed
     // let too_long_tuple = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13);
     // println!("too long tuple: {:?}", too_long_tuple);
     // TODO ^ Uncomment the above 2 lines to see the compiler error