Added information about broadcom wifi cards to readme for apple macbook pro 11.5

[igor-semyonov]

Description of changes

On a fresh install on an apple macbook pro 11.5 wifi did not work for me, but it worked fine in the live environment.
After testing, I found the following settings to work for my laptop with the broadcom BCM 43602 wifi card.

  hardware = {
    enableAllFirmware = true;
    enableAllHardware = true;
  };
  networking = {
    # This will set networking.wireless.enable to true and networking.wireless.iwd.enable to true, which turns off wpa_supplicant in favor of iwd.
    networkmanager.wifi.backend = "iwd";
  };
  boot = {
    kernelParams = [
      "brcmfmac.feature_disable=0x82000"
    ];
    # this will disable hardware-based roaming in favor of the kernel managind roaming between mesh nodes.
    extraModprobeConfig = ''
      options brcmfmac roamoff=1
    '';
  };

This is not necessarily a minimal set, but it is a working one.
I have added this information to the readme. Since using these settings depends on which wifi chip is present in the laptop, it does not seem appropriate to make these changes in the default.nix of this module. It may make sense to add a submodule for the 43602 wifi card so users can opt in to these choices without having to copy them.

Things done

• Tested the changes in your own NixOS Configuration
• Tested the changes end-to-end by using your fork of nixos-hardware and
  importing it via <nixos-hardware> or Flake input