add warning to version 2 pages

Author: keithamus

docs/_layouts/guide.html

@@ -22,6 +22,13 @@
 
   <section class="col-lg-9 px-5 f4">
     <div class="container-md markdown-body mb-5">
+      {% if page.version == 2 %}
+      <div class="flash flash-warn">
+        You are reading the documentation for the <strong>Alpha</strong> version of Catalyst. The API and documentation is subject to change.
+        The documentation for the stable version can <a href="{{ site.baseurl }}/guide/introduction">be found here</a>.
+      </div>
+      {% endif %}
+
       <h1 class="mb-4 f0-light">{{ page.title }}</h1>
       {{ content }}
       <div class="mt-4">