manual: Show copyright information not just in the printed manual

@insertcopying was not used at all in the Info and HTML versions.
As a result, the notices that need to be present according to the
GNU Free Documentation License were missing.

This commit shows these notices above the table of contents in the
HTML version, and as part of the Main Menu node in the Info version.

Remove the "This file documents" line because it is redundant with the
following line.

Tested-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>