Fix governance design

Let the governance use the default layout (all markdown files default to
"docs").

Make the default layout use the right div classes so the CSS can take
hold.

Fix the `layout` declaration for Markdown documents that are not `kind:
article`. Declare the governance to use the "default" layout, not the
"docs" one. This is the minimal change to support the governance
document. The layout choice needs a refactoring, but how to do that
needs more thought.

Rules

@@ -66,7 +66,8 @@ compile '*' do
     if item[:kind] == 'article'
       layout 'blog'
     else
-      layout 'docs'
+      # TODO(mr): separate layout selection from Markdown handling
+      layout item[:layout] || 'docs'
     end
   elsif item[:extension] == 'css'
     # don’t filter stylesheets

content/governance.md

 ---
 title: Governance
+layout: default
 
 ---
 

layouts/default.html

 <%= render 'header' %>
 
 <div class="container">
+    <div class="col-md-12 doc-content">
       <%= yield %>
+    </div>
   <%= render 'container_footer' %>
 </div>