Add logo to .navbar-brand.

Author: Florian Kissling

docs/_includes/navigation.html

@@ -7,7 +7,7 @@
         <span class="icon-bar middle-bar"></span>
         <span class="icon-bar bottom-bar"></span>
       </button>
-      <a href="./" class="navbar-brand">Select2</a>
+      <a href="./" class="navbar-brand"><img src="/images/logo.png" height="20px"> Select2</a>
     </div>
 
     <nav class="collapse navbar-collapse select2-navbar-collapse" role="navigation">