How to Send an "Add to Calendar" Link in Your Event Email
For Gmail calendar, click "Edit" to open the event in a new window, and then select the "More actions" dropdown. From there, click "Publish event":
In the pop-up screen, you'll see an HTML code or a link to the event. Simply click "Copy" beside the link to copy the link, and then open the email you intend to send and paste the URL.