add image builder notes

active/software_osbuild/image_builder.md

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+# Image Builder
+
+<https://osbuild.org/docs/user-guide/blueprint-reference/>
+
+## Warning
+
+From the [Red Hat
+Documentation](https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html-single/composing_installing_and_managing_rhel_for_edge_images/index):
+
+> You cannot build an operating system image that differs from the RHEL image
+> builder host. For example, you cannot use a RHEL system to build Fedora or
+> CentOS images.
+
+## Installing
+
+```bash
+# Install the packages
+dnf install -y osbuild-composer composer-cli
+
+# Start/enable the service
+systemctl enable --now osbuild-composer.socket
+
+# Optional: add your user to the weldr group
+sudo usermod -aG weldr $USER
+
+# Optional: cockpit dependency
+dnf install -y cockpit-composer
+```
+
+## Building Images
+
+1. Create a toml file describing your image
+
+    See `fedora-42-base.toml` for an example.
+
+2. Push the toml to composer
+
+    ```bash
+    composer-cli blueprints push active/software_osbuild/fedora-42-base.toml
+    
+    # List blueprints
+    composer-cli blueprints list
+    ```
+
+3. Generate the image
+
+    ```bash
+    # List image types
+    composer-cli compose types
+
+    # Build the image
+    composer-cli compose start fedora-42-base qcow2
+
+    # Check status
+    composer-cli compose status
+    ```
+
+4. Run the image
+
+    ```bash
+    # Download the image
+    composer-cli compose image --filename ~/Downloads/fedora-42-base.qcow2 image-uuid
+
+    # Test with qemu
+    qemu-kvm --name test-fedora-42-base -m 4096 -hda ~/Downloads/fedora-42-base.qcow2
+    ```