When we get to writing this page, include the following about Related Permits (rephrase as necessary):
Re: Related Permits: When you have a draft permit, you can go to this tab and select one or more permits (doesn't have to be the same permit number) and add the Supersedes relationship. Then, when your draft permit gets changed to In Effect, those permits [that you added the relationship to] will get changed to Superseded.
If your permit is already In Effect, adding the Supersedes relationship as described above won't have any effect. Only super admins should even be able to see/do this, since they are the only ones who are able to change In Effect permits.