docs: clarify README

Make the CPU output non-default, so you must specifically choose which
output you actually want.

README.md

@@ -7,24 +7,29 @@ This supports NVIDIA GPUs (using CUDA), AMD GPUs (using ROCm), and CPU compute (
 
 ### Setup
 
+First, run:
 ```bash
 git clone https://github.com/virchau13/automatic1111-webui-nix
-cd automatic1111-webui-nix
 git clone https://github.com/AUTOMATIC1111/stable-diffusion-webui
+cp automatic1111-webui-nix/*.nix stable-diffusion-webui/
+cd stable-diffusion-webui
+git add *.nix
 ```
 
-### Flakes
+After that, choose the command according to your platform:
+
+#### Flakes
 
 ```bash
-nix develop # CPU or Apple silicon
+nix develop .#cpu # CPU or Apple silicon
 nix develop .#cuda # CUDA
 nix develop .#rocm # ROCm
 ```
 
-### Non-flakes
+#### Non-flakes
 
 ```bash
-nix-shell # CPU
+nix-shell --argstr variant CPU # CPU
 nix-shell --argstr variant CUDA # CUDA
 nix-shell --argstr variant ROCM # ROCm
 ```
@@ -52,5 +57,5 @@ Run `./webui.sh --xformers` to set up xformers. If this command fails, try git p
 ## Credits
 - AUTOMATIC1111 for obvious reasons.
 - rprospero for [ROCm support](https://github.com/virchau13/automatic1111-webui-nix/pull/3).
-- Cloudef for [CPU compute / Apple Silicon support](https://github.com/virchau13/automatic1111-webui-nix/pull/10)
+- Cloudef for [CPU compute / Apple Silicon support](https://github.com/virchau13/automatic1111-webui-nix/pull/10).
 - polypoyo for [the original draft of this](https://github.com/AUTOMATIC1111/stable-diffusion-webui/pull/4736).

flake.nix

@@ -13,7 +13,8 @@
                 config.allowUnfree = true;
             };
         in {
-            devShells.default = import ./impl.nix { inherit pkgs; variant = "CPU"; };
+            devShells.default = throw "You need to specify which output you want: CPU, ROCm, or CUDA.";
+            devShells.cpu = import ./impl.nix { inherit pkgs; variant = "CPU"; };
             devShells.cuda = import ./impl.nix { inherit pkgs; variant = "CUDA"; };
             devShells.rocm = import ./impl.nix { inherit pkgs; variant = "ROCM"; };
         }

impl.nix

@@ -1,4 +1,4 @@
-{ pkgs, variant ? "CUDA", ... }:
+{ pkgs, variant, ... }:
 
 let
   hardware_deps = with pkgs;
@@ -19,7 +19,8 @@ let
     ] else if variant == "ROCM" then [
       rocmPackages.rocm-runtime
       pciutils
-    ] else [];
+    ] else if variant == "CPU" then [
+    ] else throw "You need to specify which variant you want: CPU, ROCm, or CUDA.";
 
 in
 pkgs.mkShell rec {

shell.nix

@@ -1,4 +1,4 @@
-{ variant ? "CUDA" }:
+{ variant ? "NONE" }:
 
 let pkgs = import <nixpkgs> { };
 in import ./impl.nix { inherit pkgs variant; }