message: not just 404
diff: @@ -320,7 +320,9 @@ visit the registry's website to obtain a token, and Cargo can store the token
  using the [`cargo login`] command, or by passing the token on the
  command-line.
  -Responses should use the 200 or 404 response code as appropriate. Failure
  +Responses use the 200 response code for success.
  +Errors should use an appropriate response code, such as 404.
  +Failure
  responses should have a JSON object with the following structure:
  ```javascript
  