There is the manpage hier(7), which describes the directory layout of a running NetBSD system.
 To make it easier for beginners to find things inside src, an equivalent document for the sources of NetBSD would be required.

Even if you're not fond with mdoc, researching this and gathering the information (e.g. in plain ASCII or markdown) would be a great benefit, and somebody who likes mdoc can then convert it to a system manpage.