Added reference to source of code

Signed-off-by: George Araújo <george.gcac@gmail.com>

_layouts/base.liquid

@@ -48,6 +48,7 @@
     </h2>
 
     <!-- Toogle language -->
+    <!-- based on https://github.com/george-gca/multi-language-al-folio/blob/main/_includes/header.liquid -->
     {% if site.languages.size >= 2 %}
       {% if site.languages.size == 2 %}
         {% if site.active_lang == site.languages.first %}