[SSSD] [sssd PR#8] MAN: Document the ldap_user_gid_number option (comment)

[fidencio]

jhrozek commented on a pull request

"""
CI: http://sssd-ci.duckdns.org/logs/job/52/87/summary.html
"""

See the full comment at https://github.com/SSSD/sssd/pull/8#issuecomment-244052362