Update guides to using wedges.

[Ahi Brown <ahibrown%yahoo.co.uk@localhost>]

Hi.

 I didn't get my NetBSD 9.0 amd64 install booting from the hard drive but on some tutorials (this one as an example https://www.netbsd.org/docs/misc/index.html#moving-usr).

 The tutorial seems to use partitions instead of wedges (slices???) which when jumping between pages and how-tos, I get some using /dev/dkx and then others doing /dev/wd0x or /dev/sd0x maybe an example of each for beginners like me?

 Thanks