added hackerrank social media network (daattali#978)

Author: tanersekmen

_config.yml

@@ -65,6 +65,7 @@ social-network-links:
 #  google-scholar: your google scholar
 #  discord: invite/invite_code or users/userid 
 #  kaggle: yourname
+#  hackerrank: yourname
 
 # If you want your website to generate an RSS feed, provide a description
 # The URL for the feed will be https://<your_website>/feed.xml

_includes/social-networks-links.html

@@ -324,4 +324,16 @@
   </li>
 {%- endif -%}
 
+{%- if site.social-network-links.hackerrank -%}
+  <li class="list-inline-item">
+    <a href="https://www.hackerrank.com/{{ site.social-network-links.hackerrank }}" title="Hackerrank">
+      <span class="fa-stack fa-lg" aria-hidden="true">
+        <i class="fas fa-circle fa-stack-2x"></i>
+        <i class="fab fa-hackerrank fa-stack-1x fa-inverse"></i>
+      </span>
+      <span class="sr-only">Hackerrank</span>
+   </a>
+  </li>
+{%- endif -%}
+
 </ul>