Use srcset for examples too.

site/docs/4.1/examples/index.html

@@ -15,7 +15,9 @@ redirect_from:
     {% if forloop.first %}<div class="row">{% endif %}
       <div class="col-sm-6 col-md-4 col-xl-3 mb-3">
         <a href="{{ site.baseurl }}/docs/{{ site.docs_version }}/examples/{{ example.name | slugify }}/">
-          <img class="img-thumbnail mb-3" src="{{ site.baseurl }}/docs/{{ site.docs_version }}/examples/screenshots/{{ example.name | slugify }}.png" alt="{{ example.name }} screenshot" width="960" height="600">
+          <img class="img-thumbnail mb-3" srcset="{{ site.baseurl }}/docs/{{ site.docs_version }}/examples/screenshots/{{ example.name | slugify }}.png,
+                                                  {{ site.baseurl }}/docs/{{ site.docs_version }}/examples/screenshots/{{ example.name | slugify }}@2x.png 2x"
+                                          src="{{ site.baseurl }}/docs/{{ site.docs_version }}/examples/screenshots/{{ example.name | slugify }}.png" alt="{{ example.name }} screenshot" width="480" height="300">
           <h5 class="mb-1">{{ example.name }}</h5>
         </a>
         <p class="text-muted">{{ example.description }}</p>