Add documentation for rendering simple cms pages in menu.

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes #334 #90
| Applies to    | ~1.0
| Fixed tickets | #334 
yeah, ben you are right for the simplecms. here we extend the phpcr-odm route document with the page document, so no point in having a model. without multiple inheritance, this would just mean a lot more copy-paste.