Fix parameter names in documentation: passwd doesn't exist anymore

Document including one playbook inside another

Fix priv argument in postgresql_user example.

add backup option to the copy modules docs

Pair of trivial documentation fixes

Small fix in documentation for seliux module

Should be "priv", not "privs". Was correct in table, but wrong in
examples.

nagios module should advertise 'services' attribute as required.

Fixed typo un user

In playbook users is not valid, please change to user.