Update formatted print activity instruction

By reading "add a macro" I first thought I am supposed to implement a new macro :)

Author: michallepicki

src/hello/print.md

@@ -74,7 +74,7 @@ Implementing the `fmt::Display` trait automatically implements the
 
  * Fix the two issues in the above code (see FIXME) so that it runs without
    error.
- * Add a `println!` macro that prints: `Pi is roughly 3.142` by controlling
+ * Add a `println!` macro call that prints: `Pi is roughly 3.142` by controlling
    the number of decimal places shown. For the purposes of this exercise,
    use `let pi = 3.141592` as an estimate for pi. (Hint: you may need to
    check the [`std::fmt`][fmt] documentation for setting the number of