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.