HTML inside a MultiFieldPanel

How to add a custom html just next to a FieldPanel, or inside a MultiFieldPanel?

the goal is to show a link next to a field in the wagtail admin.

example code

MultiFieldPanel(
            [

         FieldPanel('related_category',widget=Select2Widget),
         HTMLPanel('<a href="...">...</a>')
            ],
            heading="CATEGORY/SUB-CATEGORY",
            classname="collapsible collapsed"
        ),