Add Assignment and notify assignee email content

I have been asked to look at the wording that is emailed to the assignee when the add assignment task is used to assign an Incident to another analyst.

Currently if notify assignee is ticked the assignee recieves a plain text email that shows the Detail field from the add assignment window for both the subject line and body of the email.

I need to add by default at least the Incidnet number and set the Title field as the subject and leave the description as the body. however I can not find how where this email is generated in the system, what is defining the content of the emails sent for the add assignement task?

Thanks,