Filter: Can we mark indirectly reached documents as "extra" in Hugo menu?

[cagix]

It was suggested in Compiler-CampusMinden/CB-Vorlesung-Master#165 (reply in thread) that a more clear distinction should be made in the generated Hugo menu as to which pages are relevant to the exam and which are not.

Clearly, any page linked directly in the "timetable" in README.md is relevant for the exam. Pages that are only included via links on other pages should be marked as such in the Hugo menu.

Perhaps adding "[extra]" to the menu entry would help?