fix: clarify comment about tuple struct field access in testcase_list (#1876)

Author: Abhinav-ranish

src/hello/print/print_display/testcase_list.md

@@ -24,8 +24,7 @@ struct List(Vec<i32>);
 
 impl fmt::Display for List {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        // Extract the value using tuple indexing,
-        // and create a reference to `vec`.
+        // Create a reference to the Vec<i32> stored in the List struct.
         let vec = &self.0;
 
         write!(f, "[")?;