I think this is a quite common problem: There are normal products categories but also some additional CMS pages which could be included in the main shop navigation.
In some shops I have seen the solution, that content was put in a CMS block and the category switched to "display only CMS" block to resemble a navigation for the shop content.
But I do not think that this is a best practice.
Are there better workarounds in Community Edition? (I know there is a Enterprise Edition feature to do this).
Or is there a well-known open source module helping with that?