Documentation: set a !DOCTYPE for user manual
Documentation: set a !DOCTYPE for user manual

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 <6bf850fe12d8200b20c2c5f10fd4ad2667520b3e@jidanni.org>
Signed-off-by: Jonathan Nieder <b57189c5f2fd5b3daf3350a77fde90def1080fa5@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git