It's pretty simple!
First, you type the text of your comic's title - like so:
Grassblades.
Then, you highlight the text with your mouse (or touchpad or whatever), and then you click on the chain-link symbol in the toolbar at the top of the comment-.field:
Then you get a little pop-up window with a field where you paste your link, and click okay, and it magically turns your plain text into a link! Like so:
Grassblades.