add link to Haddocks

Author: ulysses4ever

_layouts/default.html

@@ -15,6 +15,7 @@ <h1 class="project-name">{{ site.title | default: site.github.repository_name }}
       <h2 class="project-tagline">{{ site.description | default: site.github.project_tagline }}</h2>
       {% if site.github.is_project_page %}
         <a href="{{ site.github.repository_url }}" class="btn">View on GitHub</a>
+        <a href="{{ site.baseurl }}/haddocks/" class="btn">API documentation</a>
       {% endif %}
       {% if site.show_downloads %}
         <a href="{{ site.github.zip_url }}" class="btn">Download .zip</a>