Added a Add overload to DeciderBuilder and made clear it supports fluent style

var strategy = new OneForOneStrategy(new DeciderBuilder()
                .Add<SomeException>(Directive.Restart)
                .Add<SomeOtherException>(Directive.Stop)
                .Add<SomeThirdException>(e => e.SomeValue ? Directive.Restart : Directive.Escalate)
                .Build());