Fixes #7636: Add Katello Disconnected user guide.

This appears to be due to the pathing defined in : /opt/rh/ruby193/root/usr/share/gems/gems/katello-2.0.0/lib/katello.rb

Without code change, this could be addressed by performing the following:
``` 
$ cd /usr/share/foreman
$ katello-disconnected setup --oauth-key=katello --oauth-secret=tuqVww9ZmSYR6ROftJNOgn1O8NDJ3jqL
```