Document the `add' command of `dbmmanage' in `dbmmanage.1' manpage.

Submitted by: David MacKenzie <djm@uu.net>
Reviewed by: Ralf S. Engelschall
PR: 3394


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@82397 13f79535-47bb-0310-9956-ffa450edef68