motivate derive a bit more

Author: steveklabnik

_posts/2017-02-02-Rust-1.15.md

@@ -33,10 +33,11 @@ struct Pet {
 }
 ```
 
-The `Debug` trait is then implemented for `Pet`. However, this only worked for
-traits provided as part of the standard library; it was not customizable. With
-Rust 1.15, it now is. That means, if you want to turn your `Pet` into JSON, it's
-as easy as adding [Serde][serde] to your `Cargo.toml`:
+The `Debug` trait is then implemented for `Pet`, with vastly less boilerplate.
+However, this only worked for traits provided as part of the standard library;
+it was not customizable. With Rust 1.15, it now is. That means, if you want to
+turn your `Pet` into JSON, it's as easy as adding [Serde][serde] to your
+`Cargo.toml`:
 
 ```toml
 [dependencies]