blog/index.md: sort to two categories

blog/index.md

@@ -7,8 +7,23 @@ permalink: /blog/
 Some kind of version of my blog might come here and if it does, Tumblr
 reblogs etc. are not included.
 
+*There are no uncategorized posts here so I will notice if I forget
+to put post into either category.*
+
+## English
+
 <ul>
-  {% for post in site.posts %}
+  {% for post in site.categories.english %}
+    <li>
+      <a href="{{ post.url }}">{{ post.title }}</a>
+    </li>
+  {% endfor %}
+</ul>
+
+## Finnish
+
+<ul>
+  {% for post in site.categories.finnish %}
     <li>
       <a href="{{ post.url }}">{{ post.title }}</a>
     </li>