There are a couple of ways that you can add a link to an automated message.

If you would like to simply add the link address, you can paste or type it into the message field.

Otherwise, when you click on the body field of an automated communication, a list of editing options will  be available at the top. If you would like an image or particular words to have the link connected to them, you can highlight the words/image that you want to include the link, then click on the Link tool/icon. A popup will appear, where you can add the URL address and then click OK.

Add whatever else you would like in the communication, and Save.

When the communication is sent, it will have that hyperlink within the message.