Added Mastodon to social (alshedivat#974)

Author: brunovianna

_config.yml

@@ -70,6 +70,8 @@ og_image: # The site-wide (default for all links) Open Graph preview image
 github_username: # your GitHub user name
 gitlab_username: # your GitLab user name
 twitter_username: # your Twitter handle
+mastodon_username: # your mastodon username
+mastodon_instance: # your mastodon instance
 linkedin_username: # your LinkedIn user name
 scholar_userid: # your Google Scholar ID
 semanticscholar_id: # your Semantic Scholar ID

_includes/social.html

@@ -28,6 +28,9 @@
             {%- if site.twitter_username -%}
             <a href="https://twitter.com/{{ site.twitter_username }}" title="Twitter"><i class="fab fa-twitter"></i></a>
             {% endif %}
+            {%- if site.mastodon_instance and site.mastodon_username -%}
+            <a rel="me" href="https://{{ site.mastodon_instance  }}/@{{site.mastodon_username}}" title="Mastodon"><i class="fab fa-mastodon"></i></a>
+            {% endif %}
             {%- if site.medium_username -%}
             <a href="https://medium.com/@{{ site.medium_username }}" title="Medium"><i class="fab fa-medium"></i></a>
             {% endif %}