The mail generated by the Job Notification system is predefined and AFAIK it can't be changed. The only way to accomplish your request is to create your own messaging system with sp_send_dbmail as Neeraj Dwivedi already suggested.

You could add this as a job step to your existing job or you could create a new job that periodically queries the job-history table and use sp_send_dbmail to sent the results. Keep in mind that this last option creates latency between the end of a job and the sending of the mail.