docs/182872: [patch] add updated iconv information to the porter's handbook.

[Guido Falsi]

Hi,

I filed the PR in subject to add a chapter regarding the iconv changes 
in 10 regarding to the ports tree.

I'd really like to have these included in the documentation before 10.0 
is released.

Is there someone who can review and approve this patch?

I'm, obviously, available for any discussion and to make any needed 
changes to the patch to make ti acceptable to the documentation project.

Thanks in advance!

-- 
Guido Falsi <madpilot at FreeBSD.org>