Add FilterOnFallbackPort documentation

[Arkatufus]

Running Clustered Nodes on a Single Machine

When developing or testing, you may need to run multiple Akka.NET nodes on the same host. Manually assigning distinct remote port for each process can work for a fixed seed-node strategy, but doing so for management ports would not work with Akka.Discovery and Akka.Management.Cluster.Bootstrap.

Cluster.Bootstrap expects that all hosts have the same management port. When Akka.Discovery returns a list of open ports on a host, the bootstrap coordinator will filter out any ports that are different from the locally configured management port, ignoring the rest.

To allow each host to advertise its own management port without filtering each other out, disable fallback-port filtering:

builder.WithClusterBootstrap(setup =>
{
    setup.ContactPoint.FilterOnFallbackPort = false;
});

akka.management {
  cluster.bootstrap {
    contact-point {
      # allow discovery to return multiple ports per host
      filter-on-fallback-port = false 
    }
  }
}

[Aaronontheweb]

Minor grammar fixes

[Aaronontheweb]

LGTM