Add an example for navigation within the site

Some of this is based on the presentation at the dev meeting and it may be that I've misunderstood it.

The top navigation in line with the brand and download button is to be used for inter-portal navigation, which makes sense, but I also saw a design for the dev portal that underneath the purple block at the top of the page had navigation to move between sections of the portal. Can an example for this be added to the styleguide? It doesn't seem to be implemented in any of the nav CSS classes in the CSS.

This would be used for metrics to move between "Analysis, News, Sources, etc.".