Document expected log noise

Explain the benign PCI/SELinux log entries and ignore local log files in git.

README.md

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+# banger
+
+Minimal Firecracker launcher.
+
+## Requirements
+- Linux host with KVM (`/dev/kvm` access)
+- `sudo`, `ip`, `curl`, `ssh`
+
+## Files
+- `firecracker`: Firecracker binary
+- `vmlinux`: guest kernel
+- `rootfs.ext4`: guest root filesystem
+- `id_ed25519`: SSH key for `root`
+
+## Run
+```
+./run.sh
+```
+
+## SSH
+```
+ssh -i "./id_ed25519" root@<guest_ip>
+```
+
+## Shutdown
+```
+reboot
+```
+
+## Log Notes
+- `PCI: Fatal: No config space access function found` and `MissingAddressRange` lines are expected with `pci=off` in `run.sh`.
+- `SELinux: Could not open policy file ...` is expected in the minimal rootfs.