Fixing documentation

[Trustin Lee (이희승)]

In the IRC channel:

<appel> Funny thing about documentation, it sometimes just ASSUMES
that you know this basic knowledge. The pipeline graph is confusing
also: http://www.jboss.org/file-access/default/members/netty/freezone/api/3.1/org/jboss/netty/channel/ChannelPipeline.html

Please let me know WHAT the missing basic knowledge is.  Also, the
pipeline graph could be improved if you give me more specific feed
back.  Why does it confuse you?  Is it missing something or ..?

I hope you read most hyperlinked Javadocs about the related types such
as ChannelEvent and ChannelUpstream/DownstreamHandler.  If there's
still some missing pieces, we can fill them in.

— Trustin Lee, http://gleamynode.net/