There should be a way to link an article to a Service Item. That way, if you create an article to explain a form in more detail (like an Incident) the article shows up on the right hand panel for the customer to see so they are able to clearly see there is a related article for the form. It should be expandable / able to be opened in a different tab. If it is expandable, it means the customer can look at it side by side with the form and be able to follow along while submitting the form.
This could also be used to share useful links for the form and allow a clearer instructions for customers.
But same goes the other way. You should be able to link a form to an article so that if a customer looks up and finds a published to the portal form then it can be linked and create a cyclical link form available from the article and article available from the form.