Add README.md to ODroid M1 per feedback

hardkernel/odroid-m1/README.md

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+# ODroid M1
+
+Hardware support for the Hardkernel ODroid M1: https://www.hardkernel.com/shop/odroid-m1-with-8gbyte-ram/
+
+## Initial Installation
+
+This is for creating the initial image used to install to the SD Card or NVM Drive.
+
+Example `flake.nix`:
+
+```nix
+{
+  description = "SD Card Image Generator for ODroid M1";
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    nixos-hardware.url = "github:nixos/nixos-hardware/master";
+  };
+  outputs = { self, nixpkgs, nixos-hardware }: rec {
+    nixosConfigurations.m1 = nixpkgs.lib.nixosSystem {
+      modules = [
+        "${nixpkgs}/nixos/modules/installer/sd-card/sd-image-aarch64.nix"
+        nixos-hardware.nixosModules.hardkernel-odroid-m1
+        ./sdimageconfiguration.nix
+        {
+          nixpkgs.config.allowUnsupportedSystem = true;
+          nixpkgs.hostPlatform.system = "aarch64-linux";
+          nixpkgs.buildPlatform.system = "x86_64-linux"; # If you build on x86 otherwise change this.
+        }
+      ];
+    };
+    images.m1 = nixosConfigurations.m1.config.system.build.sdImage;
+  };
+}
+```
+
+For building the initial sd card image, you can use this example (tweaked for your preferences) `sdimageconfiguration.nix`:
+
+```nix
+{ config, pkgs, lib, ... }:
+
+{
+  system.stateVersion = lib.mkDefault "25.11";
+  nixpkgs.hostPlatform.system = "aarch64-linux";
+
+  sdImage = {
+    # Skip compression, we'll want the img uncompressed for flashing anyway
+    compressImage = false;
+    # The system will not boot if this is missing
+    populateRootCommands = ''
+      ${config.boot.loader.petitboot.populateCmd} -c ${config.system.build.toplevel} -d ./files/kboot.conf
+    '';
+  };
+
+  services.openssh = {
+    enable = true;
+    settings = {
+      # Highly recommended: Set Password Authentication to false if you have authorized keys you can use. This is an insecure default
+      PasswordAuthentication = true;
+      PermitRootLogin = "no";
+      AllowUsers = [ "odroid" ];
+    };
+  };
+
+  # You will almost certainly want Git to pull in your configuration repository
+  environment.systemPackages = [
+    pkgs.git
+  ];
+
+  users.users.odroid = {
+    isNormalUser = true;
+    description = "Default User";
+    extraGroups = [ "networkmanager" "wheel" ];
+    packages = [];
+    # Highly recommended: Change this default password using `sudo passwd` after logging in
+    initialPassword = lib.mkForce "odroid";
+    # You can find this from https://github.com/username.keys for example
+    openssh.authorizedKeys.keys = [];
+  };
+}
+```
+
+Put both of these files into a Git repo, and build with:
+
+```sh
+nix build .#images.m1
+```
+
+## Ongoing updates
+
+To your NixOS server flake, you'll want to ensure that the host is set to aarch64-linux.
+
+An example flake:
+
+```nix
+{
+  description = "My NixOS configuration flake";
+
+  inputs = {
+    # Nixpkgs - Stable 25.11 release
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
+    # Home Manager - Stable 25.11 release
+    home-manager.url = "github:nix-community/home-manager/release-25.11";
+    home-manager.inputs.nixpkgs.follows = "nixpkgs";
+    # NixOS Hardware
+    nixos-hardware.url = "github:nixos/nixos-hardware/master";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    home-manager,
+    nixos-hardware,
+    ...
+  }@inputs:
+
+  let
+    mkSystem = hostname: systemArchitecture: # hostname: is a positional argument
+      nixpkgs.lib.nixosSystem {
+        system = systemArchitecture;
+
+        specialArgs = { inherit inputs; };
+
+        modules = [
+          ./hosts/${hostname}/configuration.nix
+
+          home-manager.nixosModules.home-manager
+          {
+            home-manager.useGlobalPkgs = true;
+            home-manager.useUserPackages = true;
+            home-manager.backupFileExtension = "backup";
+          }
+        ];
+      };
+
+    hosts = [
+      { hostname = "other-example"; systemArchitecture = "x86_64-linux"; }
+      { hostname = "odroid-m1-example"; systemArchitecture = "aarch64-linux"; }
+    ];
+  in
+  {
+    # This is what creates the NixOS configurations for each host
+    nixosConfigurations = builtins.listToAttrs (
+      # Iterator - nixConfigurations.<name> = <value>
+      map (host: {
+        name = host.hostname;
+        value = mkSystem host.hostname host.systemArchitecture;
+      })
+      # Array to iterate over
+      hosts
+    );
+  };
+}
+```
+
+And the related `configuration.nix`:
+
+```nix
+{ config, pkgs, inputs, ... }:
+
+{
+  imports =
+    [
+      inputs.nixos-hardware.nixosModules.hardkernel-odroid-m1
+      ./hardware-configuration.nix
+      ../../modules/nix
+      ../../users
+    ];
+
+  networking.hostName = "odroid-m1-example"; # Define your hostname.
+}
+```
+
+And `hardware-configuration.nix`:
+
+```nix
+# Do not modify this file!  It was generated by ‘nixos-generate-config’
+# and may be overwritten by future invocations.  Please make changes
+# to /etc/nixos/configuration.nix instead.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports =
+    [ (modulesPath + "/installer/scan/not-detected.nix")
+    ];
+
+  boot.initrd.availableKernelModules = [ "nvme" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  fileSystems."/" =
+    { device = "/dev/disk/by-uuid/44444444-4444-4444-8888-888888888888";
+      fsType = "ext4";
+    };
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "aarch64-linux";
+}
+```
+
+You can generate these default files (with a few warnings) by running the following command on the odroid after initial boot:
+
+```sh
+nixos-generate-config
+```
+
+It will save a configuration.nix and hardware-configuration.nix to `/etc/nixos`. Critically, you will need to add `inputs.nixos-hardware.nixosModules.hardkernel-odroid-m1` to the imports in `configuration.nix` for it to work.