Added a new section to the intro chapter of the user manual for the multi-processor framework.
This is just a light description and pointer to Gary's official announcement at
https://mail.gna.org/public/relax-devel/2007-05/msg00000.html (Message-id:
<463B2E31.30503@...>). In the future this should be expanded into its own chapter and
include an extensive description with most of the text of the mailing list message.
