Update compiler/rustc_error_codes/src/error_codes/E0120.md

Co-authored-by: Trevor Gross <t.gross35@gmail.com>

compiler/rustc_error_codes/src/error_codes/E0120.md

@@ -1,4 +1,4 @@
-Drop was implemented on a trait object or reference, which is not allowed; only
+`Drop` was implemented on a trait object or reference, which is not allowed; only
 structs, enums, and unions can implement Drop.
 
 Erroneous code examples:
@@ -19,8 +19,8 @@ impl Drop for &'_ mut Concrete  {
 }
 ```
 
-A workaround for traits is to wrap the trait up in a struct, and implement
-Drop on that:
+A workaround for traits is to create a wrapper struct with a generic type,
+add a trait bound to the type, and implement `Drop` on the wrapper:
 
 ```
 trait MyTrait {}
@@ -32,13 +32,13 @@ impl <T: MyTrait> Drop for MyWrapper<T> {
 
 ```
 
-Alternatively, wrapping trait objects requires something:
+Alternatively, `Drop` can be implemented on trait objects:
 
 ```
 trait MyTrait {}
 
-//or Box<MyTrait>, if you wanted an owned trait object
-struct MyWrapper<'a> { foo: &'a MyTrait }
+// or Box<dyn MyTrait>, if you wanted an owned trait object
+struct MyWrapper<'a> { foo: &'a dyn MyTrait }
 
 impl <'a> Drop for MyWrapper<'a> {
     fn drop(&mut self) {}