[PATCH] manual: Show copyright information not just in the printed manual

[Florian Weimer]

* Florian Weimer via Libc-alpha:

> @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 redudant with the
> following line.

Ping.  This patch needs review:

  <https://sourceware.org/pipermail/libc-alpha/2020-May/114314.html>

Thanks,
Florian