(chore): fix the home navigation url

Making home navigation url to be using `{{site.url}}` variable

Closes #93

Author: kameshsampath

supplemental-ui/partials/header-content.hbs

@@ -2,7 +2,7 @@
   <nav class="navbar">
     <div class="navbar-brand">
       <div class="navbar-item">
-        <a href="/">Knative Tutorial</a>
+        <a href="{{site.url}}">Knative Tutorial</a>
       </div>
       <button class="navbar-burger" data-target="topbar-nav">
         <span></span>