Improved category name for reading optimisation

Signed-off-by: Jim Martens <github@2martens.de>

_layouts/post.html

@@ -1,12 +1,13 @@
 ---
 layout: default
 ---
+
 {% if page.date_modified %}
 {% assign modified = page.date_modified %}
 {% else %}
 {% assign modified = page.date %}
 {% endif %}
-<article class="post" itemscope itemtype="http://schema.org/BlogPosting">
+<article class="post reading-optimised" itemscope itemtype="http://schema.org/BlogPosting">
 
     <header class="post-header">
         <h1 class="post-title" itemprop="name headline">{{ page.title }}</h1>