Install documentation

[Arto Huusko <arto.huusko%pp.qnet.fi@localhost>]

Someone might want to do some update work on the installation
doc: it claims that to rebuild the system all the source sets
except secrsrc.tgz are needed. This is not true, sharesrc and
syssrc are enough.

Also advised size for usr is 95 Mb. I put it to 180mb and
even without X after installing sys and sharesrc (and NetBSD 1.3,
of course) usr had only 30 Mb free. Some one get disappointed.

-- 
         Arto Huusko
E-Mail : arto.huusko%pp.qnet.fi@localhost
WWW URL: www.qnet.fi/ahuusko/