Stub out the send letters page

app/templates/views/letters.html

@@ -0,0 +1,17 @@
+{% extends "withnav_template.html" %}
+
+{% block page_title %}
+  Send letters – GOV.UK Notify
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  <h1 class="heading-large">
+    Send letters
+  </h1>
+
+  <p>
+    This page is where you would go to send letters.
+  </p>
+
+{% endblock %}