add BMBF logo to main page pug

Author: lkeegan

src/pug/index.pug

@@ -22,3 +22,6 @@ block content
           if index == 1
             +index_card_downloads
           +index_card(card.title, card.icon, card.url, card.links)
+  section.pt-4
+    .container.text-center
+      img.w-25(src="assets/BMBF_logo_en.jpeg", alt="BMBF logo")