Add a missing manualdir entry in the Debian layout.

Submitted by:	Thom May <thom@planetarytramp.net>
Reviewed by:	Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93818 13f79535-47bb-0310-9956-ffa450edef68