Log Message:
doc/guide/ftp-layout.xml: Catch up to modern reality

We don't have builds from date-based checkouts, or 4.99.x.
Mention that there are READMEs within ftp.

CVS: ----------------------------------------------------------------------
CVS: CVSROOT  cvs.NetBSD.org:/cvsroot
CVS: please use "PR category/123" to have the commitmsg appended to PR 123