Better documentation for rvd_back command line options

[dani-sanchez-dorado]

Some command line options of the rvd_back command line are indocumented.
Add documentation for this options whould will improve the whole project.

This opcions have explanation, but no appear in "rvd_back --help" command list:

• [--add-group-ldap]
• [--remove-group-ldap]
• [--add-user-group ]
• [--import-domain ]
• [--import-domain-owner ]
• [--url-isos ]
• [ --add-locale-repository LOCALE ]

This options appear in command line, but has no help text:

• [--debug]
• [--test-ldap]
• [-X]
• [--rebase MACHINE]

I think that whould be very interesting add the "rvd_back --help" to documentation because then whould be very easy find this opcions in the "read the docs" search or simply googling it .

Thanks in advance!