Add tweet card image (if any) to the timeline RSS feed. (#438)

src/views/rss.nimf

@@ -44,6 +44,11 @@ Twitter feed for: ${desc}. Generated by ${cfg.hostname}
 #  let url = &"{urlPrefix}{getPicUrl(get(tweet.gif).url)}"
 <video poster="${thumb}" autoplay muted loop style="max-width:250px;">
   <source src="${url}" type="video/mp4"</source></video>
+#elif tweet.card.isSome:
+#  let card = tweet.card.get()
+#  if card.image.len > 0:
+<img src="${urlPrefix}${getPicUrl(card.image)}" style="max-width:250px;" />
+#  end if
 #end if
 #end proc
 #