Update `resource check container` section to reflect global resources

[Ciro S. Costa]

With the introduction of Global Resources, it's not true anymore that there's a 1:1 mapping of resource_config and number of check containers as documented in Resource Check Container section - the mapping is in terms of resource_config_scopes (please correct me if I'm wrong).

For those aiming at better understand the number of check containers they have, such not up-to-date documentation might be misleading.

Thanks!