add PS5 kernel build pipeline with multi-distro support and arm64 cross-compile

README.md

@@ -47,6 +47,8 @@ sudo dd if=output/ps5-ubuntu2604.img of=/dev/sdX bs=4M status=progress
 | `--kernel` | Path to kernel source directory | auto-clone `v6.19.10` |
 | `--img-size` | Disk image size in MB | `12000` (`32000` for `all`) |
 | `--clean` | Remove all cached build artifacts and start fresh | off |
+| `--kernel-only` | Build and package the kernel only, then exit | off |
+| `--patches-ref` | Branch, tag, or commit SHA for patches | `v1.0` |
 
 ## Caching
 
@@ -105,10 +107,27 @@ All verbose output goes to `build.log`. The terminal shows a spinner with live p
 
 The boot partition contains kexec scripts to switch between distros at runtime. Ubuntu 26.04 is the default boot target.
 
+## Building the Kernel Standalone
+
+Use `--kernel-only` to compile the PS5 kernel and produce installable packages without building a full disk image.
+
+```bash
+./build_image.sh --kernel-only                                # .deb (default)
+./build_image.sh --kernel-only --distro all                   # .deb + .pkg.tar.zst
+./build_image.sh --kernel-only --patches-ref main             # fetch from specific branch/tag
+./build_image.sh --kernel-only --clean                        # wipe and rebuild from scratch
+```
+
+Output packages are written to `linux-bin/`. Install on a running PS5 Linux system:
+
+```bash
+sudo dpkg -i linux-bin/linux-ps5_*.deb
+```
+
 ## Directory Layout
 
 ```
-build_image.sh                  # Main build script
+build_image.sh                  # Image builder (also supports --kernel-only)
 docker/
   kernel-builder/               # Kernel compilation container
   kernel-builder-arch/         # Repackages .deb kernel as .pkg.tar.zst