[bug-inetutils] manual fixes

[Simon Josefsson]

FYI, I noticed the indices in the manual were broken.  Everything was
under the 'Concept Index' node and the 'Index' node was empty.  The
descriptions in each chapter was wrong.  At the top of the file, all
indexes were merged, which is typical, so I just fixed the rendering of
it.

I also made the Introduction section a bit more friendly.  At least the
first sentence doesn't have to be that the manual is work in progress.
Browsing through the manual, I don't think we are that bad off actually,
and maybe we could even go through it and check for omissions and remove
the 'work in progress' denimisher.

/Simon