don't use sentence fragments, make the docs searchable

don't use sentence fragments, make the docs searchable

Hi all,

Here's a patch to userdir-ldap-cgi to improve the documentation in
doc-mail.wml:

 Replace the sentence fragment at the beginning of the documentation on
 DNS records with a complete sentence that uses the actual field name, making
 the documentation more searchable.

Signed-off-by: Martin Zobel-Helas <zobel@debian.org>