Copy insanity from scaffold.

lib/generators/simple_form/templates/_form.html.erb

@@ -1,4 +1,16 @@
 <%%= simple_form_for(@<%= singular_name %>) do |f| %>
+  <%% if @<%= singular_name %>.errors.any? %>
+    <div id="error_explanation">
+      <h2><%%= pluralize(@<%= singular_name %>.errors.count, "error") %> prohibited this <%= singular_name %> from being saved:</h2>
+
+      <ul>
+      <%% @<%= singular_name %>.errors.full_messages.each do |msg| %>
+        <li><%%= msg %></li>
+      <%% end %>
+      </ul>
+    </div>
+  <%% end %>
+
   <div class="inputs">
   <%- attributes.each do |attribute| -%>
     <%%= f.<%= attribute.reference? ? :association : :input %> :<%= attribute.name %> %>