Include LDAP OR docs from Jake Carroll

See http://lists.openmicroscopy.org.uk/pipermail/ome-users/2014-August/004629.html

Rather than reconfigure LDAP to use use [Global Catalogue](https://www.openmicroscopy.org/site/support/omero5/sysadmins/server-ldap.html?highlight=active%20directory#global-catalogue) for Active Directory, it is also possible to use explicit OUs as pointed out by Jake Carroll from UQ.