You can add custom pages like this by adding menu = "main" in the frontmatter:

+++
date  = "2015-08-22"
title = "About me"
menu  = "main"
url = "about/"
+++

This site is just a usual document. Create a new file, e.g. about.md in the content content directory. The url variable in the frontmatter allows you to define the final url of the about page.