added meta tag for google search indexing

Author: Jannik-Hm

_includes/head-custom.html

@@ -1,5 +1,7 @@
 <link href="assets/css/fontawesome.css" rel="stylesheet">
 
+<meta name="google-site-verification" content="QcqbkyN7JkilKDkP5YmwyorBYfAn2vxk3z2jOP3Xiak" />
+
 {% if site.favicon %}
   <link rel="shortcut icon" type="image/x-icon" href="{{ '/favicon.ico' | relative_url }}">
 {% endif %}