Add a page to the topnav would not correctly indicate the active page is the page is part of the course site

[dirkcuys]

The instructions tells a user how to add a item to the top navigation menu, but if a user adds a page as part of the course (as apposed to the page being external) the topnav won't correctly display the styling for the page being active when a user visits the page.

A possible solution is to add a section for extra topnav items to _data/course.yml, eg.

topnav:
- url: /facilitate
  title: Facilitate

We would need to update both the instructions and the implementation for this.