nanoBSD Doc needs updating

[Jed Clear]

Changes to the nanaoBSD script between 8.0R and 8.1R are not reflected in its handbook or man pages.  Most notably that NANO_ARCH now defaults to the build machine processor (`uname -p`), and is no longer hard coded to i386.   

And neither handbook or man page documents cust_pkg() and NANO_PACKAGE_DIR, which have been around for a bit..

And from the revision notes, it looks like NANO_LABEL has been added to -CURRENT.

-Jed