Update on NanoBSD howto

[Josmar Pierri]

Hello,

The example on NanoBSD howto on section 2.4.3 ("Using nc(1)" at 
https://www.freebsd.org/doc/en_US.ISO8859-1/articles/nanobsd/howto.html) 
should be updated to reflect the new behavior of 'nc' regarding the 
disconnection after reaching EOF, either on server and client side.

It would be better, as a complete example, if it call the 'update' 
script instead of 'updatep1' ou 'updatep2'.

An accurate example that works on FreeBSD 11 is:

	myhost# nc -l -N 2222 < _.disk.image

	# nc -d myhost 2222 | sh update

It may also help having a little note saying that will be required to 
press F1 or F2 on next boot, in order to actually use the new image.