open-webui-oci: replace version with image option

docs/modules/nixos/open-webui-oci.md

@@ -9,19 +9,33 @@ View the [*synix* NixOS module on Forgejo](https://git.sid.ovh/sid/synix/tree/ma
 - [Homepage](https://openwebui.com/)
 - [GitHub](https://github.com/open-webui/open-webui)
 - [Environment Configuration](https://docs.openwebui.com/getting-started/env-configuration/)
+- [Nixpkgs Docker tools](https://github.com/NixOS/nixpkgs/blob/master/doc/build-helpers/images/dockertools.section.md)
 
 ## Configuration
 
 ```nix
-{ inputs, ... }:
-
 {
   imports = [ inputs.synix.nixosModules.open-webui-oci ];
 
   services.open-webui-oci.enable = true;
+
+  # You can provide an image to use:
+  services.open-webui-oci.image = pkgs.dockerTools.pullImage {
+    imageName = "ghcr.io/open-webui/open-webui";
+    imageDigest = "sha256:2deb90b0423473d8f97febced2e62b8fd898aa3eb61877bb3aa336370214c258";
+    hash = "sha256-2cdKfvZGUyPUm7TFXcf5OcG9ey4BvOZPUOVim1S2C+s=";
+    finalImageName = "ghcr.io/open-webui/open-webui";
+    finalImageTag = "0.8.5";
+  };
 }
 ```
 
+You can use `nix-prefetch-docker` to get the attribute set to pass to `dockerTools.pullImage`:
+
+```bash
+nix run nixpkgs#nix-prefetch-docker -- --image-name ghcr.io/open-webui/open-webui --arch amd64 --os linux --image-tag 0.8.5
+```
+
 ## Usage
 
 Visit the web interface at your specified location to create an admin account.