Add Fathom analytics tracking script (#153)

Author: dergigi

_includes/head.html

@@ -66,6 +66,8 @@
 <link rel="alternate" type="application/rss+xml" title="{{ site.title }}" href="{{ '/feed.xml' | prepend: site.baseurl }}">
 <link rel="canonical" href="{{ page.url | replace: 'index.html', '' | prepend: site.baseurl }}">
 
+<script src="https://cdn.usefathom.com/script.js" data-site="OJAAUZLM" defer></script>
+
 {% if site.google_analytics %}
   <script>
     (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){