A minor reorganization

[Bruce Dubbs]

In conjunction with some of Alexander's proposals I would like to makes some 
changes.

Does anyone object if I move section 4.5 (About SBUs) to right after section iv 
(Host System Requirements).

I also want to rename the SBU section to "Time to Build an LFS System".  And add 
some discussion about the overall time to build.  I will suggest that ALFS can 
build a system in about two hours on a reasonably fast system, but ALFS is not 
recommended for first time LFS users.

   -- Bruce