Use the allowed example domain

This PR change the text to use the correct example domain example.org and also some minor CS issues.
I wonder if this sentence, suitably re-worded, should be moved to the top of this section.  I think most people will use their control panel or phpMyAdmin to set up the database and might be frightened off installing Joomla at all if they are not comfortable with the command line and don't read to the end of the section.  Just a thought.