Create a post announcing and explaining Kroki usage

_includes/cards/post_card.html

@@ -25,6 +25,10 @@ post: The post which sould be displayed on the card
                 <i class="fas fa-calendar-day" aria-hidden="true"></i>
                 {{ include.post.date | date: "%d.&thinsp;%b.&thinsp;%y" }}
             </span>
+            <span class="badge badge-secondary">
+                <i class="fas fa-tag" aria-hidden="true"></i>
+                {{ include.post.categories }}
+            </span>
         </div>
         <div class="card-text">
             <a href="{{ include.post.url | relative_url }}" class="stretched-link">