asciidoc already takes care of including a doctype for most of the
HTML documentation, but the user manual which is processed with
docbook-xsl directly lacks one (at least with Debian docbook-xsl
1.75.2+dfsg-5). This makes it harder to automatically validate the
HTML.
Reported-by: 積丹尼 <jidanni@jidanni.org> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>