Bug#763005: Installation guide target should not be hardcoded

[Nicolas Kuttler <nkuttler@gmail.com>]

Package: www.debian.org
Followup-For: Bug #763005

This problem still exists on the website.

https://www.debian.org/releases/stable/installmanual

leads to

https://www.debian.org/releases/stable/amd64/

which says

    This document contains installation instructions for the Debian
    GNU/Linux 9 system (codename “stretch”), for the 64-bit PC (“amd64”)

It is not clear at all if it's the wrong manual, or if it's just a wrong
string. I don't know either, but I know it's very confusing.