Add discord to supported social networks (daattali#907)

* add discord to social-networks-links.html

* Update _config.yml

* Update Discord entry

_config.yml

@@ -71,6 +71,7 @@ social-network-links:
 #  mastodon: instance.url/@username
 #  ORCID: your ORCID ID
 #  google-scholar: your google scholar
+#  discord: invite/invite_code or users/userid 
 
 # If you want to show a link to an RSS in the footer, add the site description here.
 # If you don't want to show an RSS link, remove the following line.

_includes/social-networks-links.html

@@ -299,5 +299,17 @@
    </a>
   </li>
 {%- endif -%}
+
+{%- if site.social-network-links.discord -%}
+  <li class="list-inline-item">
+    <a href="https://discord.com/{{ site.social-network-links.discord }}" title="Discord">
+      <span class="fa-stack fa-lg" aria-hidden="true">
+        <i class="fas fa-circle fa-stack-2x"></i>
+        <i class="fab fa-discord fa-stack-1x fa-inverse"></i>
+      </span>
+      <span class="sr-only">Discord</span>
+   </a>
+  </li>
+{%- endif -%}
 
 </ul>