Merge branch '9-improve-seo' into 'develop'

Resolve "Improve SEO"

See merge request R3/howto-cards!137

.gitlab-ci.yml

 # In case something goes horribly wrong, you can fall back to `image: ruby:2.5`
-image: git-r3lab.uni.lu:4567/r3/docker/jekyll-lcsb:1.4
+image: git-r3lab.uni.lu:4567/r3/docker/jekyll-lcsb:1.5
 
 stages:
   - build

_config.yml

@@ -71,6 +71,11 @@ defaults:
     values:
       include_link: true
       searchable: 1.0 
+  - scope:  # adding og:image to the SEO's metadata
+      path: ""
+    values:
+      image: /assets/favicon/apple-touch-icon.png
+
 
 
 # Exclude from processing. (no need to touch these)