adding gravity form to custom post edition

I'm not 100% sure what you are asking. Are you asking how do you insert a form into one of your custom post type pages? If so you should just use insert the Gravity Forms shortcode into the content of your custom post.

The Gravity Forms + Custom Post Types Add-On is for using Gravity Forms to CREATE custom post type posts. It's not for using Gravity Forms with Custom Post Types as far as being able to insert a form into a custom post.

The documentation to embed a form into a page or post is here, the same applies for embedding a form into a custom post:

http://www.gravityhelp.com/documentation/page/Embedding_A_Form