The user guide revised. Please review.

[Trustin Lee]

Hi,

I've just finished updating the first chapter of the user guide.  The
notable change is a new section about how to shut down properly,
because it was quite an FAQ.  Please let me know if you think
something needs to be added or updated to this first chapter:

  * http://tinyurl.com/b2snx4

Meanwhile, I will be writing the second chapter, which reveals the
details of the architecture and event model.

Cheers,

— Trustin Lee, http://gleamynode.net/