If you're interested in contributing to the developer docs for extensions (or you're just curious how it works), you've found the right place.
You can help improve the extension docs for Google Chrome in a couple of ways:
Although the doc appears to be on code.google.com, it isn't. It's really in the Chromium project and served up by an AppEngine app. To modify the doc, you need to build it.
For details on where doc content comes from (from the server's point of view), see How Extension Docs Are Served.