Crediting other creators

First you'll need to navigate to your comic's control panel. You can do so a few different ways, but for this one let's just click on the "EDIT" for that comic in the user sidebar:

You'll be taken to your comic's control panel (or the Edit Comic area). Here you'll want to click on the "credits" button:

You can use the fields to add credits. You can type whatever you like in the fields... which is useful if you need to credit different artists for different chapters, or unusual credits or situations:

(The X button deletes a credit.)

Currently the credits don't show up anywhere that other people can see them, though. (I am looking into that.)