This allows the use of header and footer partials to help aid in theming. With this you don't have to override main.mustache of you only want to inject custom CSS or JS into the default template. Just create your own selleck-head.mustache or selleck-foot.mustache and drop them into your partials folder.
This will also help in the case that you have 2 ways to display your examples (locally with the default template) and remote (with a website template) and you want them to behave differently or you need different assets in one that you do the other ;)
Ryan, feel free to drop the comments out of the partials if you want, I put them in so that they are easy to identify when looking at the markup. I could add a paragraph to the docs about it if you want.
Added custom header and footer partials for easier themeing