doc: update links for andre-simon.de

doc: update links for andre-simon.de

Beyond the fact that it's somewhat traditional to respect sites'
self-identification, it's helpful for links to point to the things
that people expect them to reference. Here that means linking to
specific pages instead of a domain.

Signed-off-by: Josh Soref <jsoref@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>