Markdown
This page lives in the /src/markdown directory.
The menu link to the page is added via the /src/site.xml file.
Maven
Here's the link to the Maven Doxia plugin for Markdown . The Doxia overview page shows using Markdown by default.
Unfortunately, there's not a lot of documentation there - but at least you have this project showing you a simple example!
These Markdwon files will automatically be turned into .html files with the matching name. For example, this overview.md file gets turned into overview.html.
Here's an example of linking to a second markdown page.
Editors
What's nice about this is that you can use one of a very large number of Markdown editors for writing your Maven documentation. Just search for Markdown editor and your platform on Google and you should find several nice ones.