Add essential initramfs integration for composefs support

- Add initramfs integration files based on debian-bootc project
- Include bootc-initramfs-setup.service for systemd integration
- Add dracut module-setup.sh for initramfs generation
- Include prepare-root.conf for OSTree composefs configuration
- Update Containerfile examples to include initramfs files
- Fix systemctl calls to use symlinks instead of systemctl commands
- Add comprehensive initramfs-integration.md documentation
- Update README to reference new initramfs documentation

Based on files from https://github.com/bootcrew/debian-bootc:
- bootc-initramfs-setup.service
- module-setup.sh
- prepare-root.conf

These files are essential for proper composefs support and boot
functionality in Debian bootc images.

building/base-images-wo-bootc.md

@@ -971,6 +971,86 @@ rm -rf "${TEMP_DIR}"
 echo "✅ Installation completed with systemd-nspawn!"
 ```
 
+## Essential Initramfs Integration
+
+For proper composefs support and boot functionality, you need to include initramfs integration files in your base image. These files are essential for Debian bootc images:
+
+### Required Files
+
+**1. `bootc-initramfs-setup.service`** - Systemd service for initramfs:
+```ini
+# Copyright (C) 2013 Colin Walters <walters@verbum.org>
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2 of the License, or (at your option) any later version.
+
+[Unit]
+DefaultDependencies=no
+ConditionKernelCommandLine=composefs
+ConditionPathExists=/etc/initrd-release
+After=sysroot.mount
+Requires=sysroot.mount
+Before=initrd-root-fs.target
+Before=initrd-switch-root.target
+OnFailure=emergency.target
+OnFailureJobMode=isolate
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/bootc-initramfs-setup
+StandardInput=null
+StandardOutput=journal
+StandardError=journal+console
+RemainAfterExit=yes
+```
+
+**2. `module-setup.sh`** - Dracut module for initramfs:
+```bash
+#!/usr/bin/bash
+check() {
+    return 0
+}
+
+depends() {
+    return 0
+}
+
+install() {
+    inst \
+        "${moddir}/bootc-initramfs-setup" /bin/bootc-initramfs-setup
+    inst \
+        "${moddir}/bootc-initramfs-setup.service" \
+        "${systemdsystemunitdir}/bootc-initramfs-setup.service"
+    $SYSTEMCTL -q --root "${initdir}" add-wants \
+        'initrd-root-fs.target' 'bootc-initramfs-setup.service'
+}
+```
+
+**3. `prepare-root.conf`** - Composefs configuration:
+```ini
+[composefs]
+enabled = yes
+
+[sysroot]
+readonly = true
+```
+
+### Integration in Containerfile
+
+Add these files to your base image:
+
+```dockerfile
+# Copy initramfs integration files
+COPY files/37composefs/bootc-initramfs-setup.service /usr/lib/systemd/system/
+COPY files/37composefs/module-setup.sh /usr/lib/dracut/modules.d/37composefs/
+COPY files/ostree/prepare-root.conf /usr/lib/ostree-boot/prepare-root.conf
+
+# Enable the service
+RUN ln -sf /usr/lib/systemd/system/bootc-initramfs-setup.service \
+    /etc/systemd/system/multi-user.target.wants/bootc-initramfs-setup.service
+```
+
 ## Adding Application Layers (Example: nginx)
 
 ### Method 1: Building on Base Image