Add message about DrupalCamp London workshop

source/_layouts/default.html.twig

@@ -5,6 +5,10 @@
 
     <div class="mt-10 container">
         <main id="main-content" class="flex-1 wrap {{ page.layout == 'front' ? 'is-wide' : '' }}">
+            {% if page.layout in ['post', 'talk'] %}
+                {% include 'site-message' %}
+            {% endif %}
+
             {% block page_title_wrapper %}
                 <h1 class="leading-tight mb-4">
                     {% block page_title %}{{ page.title }}{% endblock %}

source/_partials/site-message.html.twig

@@ -0,0 +1,4 @@
+<div class="markup mb-8 px-5 py-3 text-sm border-b-2 border-yellow-300 bg-yellow-100">
+    <p>Oliver is giving a workshop, <a href="https://opdavi.es/dclondon20">Automated Testing and Test Driven Development with Drupal 8</a>, next month at DrupalCamp London.</p>
+    <p><a href="http://opdavi.es/YilTZ" title="Find out more and register on the DrupalCamp London website">Find out more and register</a> on the DrupalCamp London website.</p>
+</div>