update README

README.md

@@ -56,11 +56,12 @@ Cargo.toml:
 diesel-derive-enum = { version = "2.1.0", features = ["postgres"] }
 ```
 
-Suppose our project has the following `diesel.toml`:
+Suppose our project has the following `diesel.toml` (as generated by `diesel setup`):
 
 ``` toml
 [print_schema]
 file = "src/schema.rs"
+custom_type_derives = ["diesel::query_builder::QueryId"]
 ```
 
 And the following SQL:
@@ -79,7 +80,7 @@ Then running `$ diesel migration run` will generate code something like:
 // src/schema.rs -- autogenerated
 
 pub mod sql_types {
-    #[derive(diesel::sql_types::SqlType)]
+    #[derive(diesel::sql_types::SqlType, diesel::query_builder::QueryId)]
     #[diesel(postgres_type(name = "my_enum"))]
     pub struct MyEnum;
 }