One slight revision to README

Hello Jason,

I followed the README to install postgresql 7.4 on my new laptop (with XP
Home), and it went very smoothly. Thank you so much.

There was only one spot where what I did deviated from the README. I don't
have a /var/postgresql directory, and mkdir /var/postgresql/data won't work
if it's not there, so maybe you want to change steps 5 and 6 to:

5. Create the PostgreSQL data directory:

# mkdir /var/postgresql
# mkdir /var/postgresql/data

6. Change ownership of the PostgreSQL data directory:

# chown postgres /var/postgresql # [10]
# chown postgres /var/postgresql/data # [10]

Or maybe that's overdoing it? Just trying to save you from the windiots
(the windows people grossly unfamiliar with unix) ...

-- Seth