I recently used PS and here is an example:
To: John CC: Many people including executives
Subject: How to build a wall
Hi John,
Attached document explains how to build a wall...
1.
2.
3.
4.
I have also added details on how to get funding...
1.
2.
3.
Thanks,
Tom
PS: I didn't have permissions to add this information to your online document and therefore I have created a separate document. Please feel free to copy/paste this information to your online document.
The main topic of the email is how to build the wall and how to get funding. Why it's not added to the online doc is trivial and most recipients of the email would not care. Therefore, I don't think it needs to be in the main body of the email.