[documentation] Mac Os Bug - explain Mac users need to use `hostname_localhost`

[jan-janssen]

Unfortunately, the MacOs Firewall is blocking connections on the users IP address, so we need to enable hostname_localhost. Still this could also be done by default, as Macs are rarely used in clusters.

[jan-janssen]

The issue is now mentioned in the documentation https://executorlib.readthedocs.io/en/latest/trouble_shooting.html#firewall-issues