docs: add full command reference; fix module path and KernelURL config

- Add docs/commands.md with per-command purpose, step-by-step shell/SDK
  call sequences, config tables, outputs, and error conditions
- Rename module from github.com/you/fc-orchestrator to github.com/kacerr/fc-orchestrator
- Add KernelURL field to Config so the download URL is configurable via
  FC_KERNEL_URL instead of being hardcoded in Init()
- Expose FC_KERNEL_URL in the usage string
- Add verbose logging of dd/mkfs.ext4/mount/tar calls in buildRootfs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

main.go

@@ -19,10 +19,17 @@ import (
 	"fmt"
 	"os"
 
-	"github.com/you/fc-orchestrator/orchestrator"
+	"github.com/kacerr/fc-orchestrator/orchestrator"
 )
 
 func main() {
+	// figure out if we are running as root
+	if os.Geteuid() == 0 {
+		fmt.Println("Running with root/sudo privileges!")
+	} else {
+		fmt.Println("Running as a normal user.")
+	}
+
 	if len(os.Args) < 2 {
 		usage()
 		os.Exit(1)
@@ -68,6 +75,7 @@ Environment:
   FC_BIN          firecracker binary path  (default: firecracker)
   FC_BASE_DIR     working directory         (default: /tmp/fc-orch)
   FC_KERNEL       vmlinux path
+  FC_KERNEL_URL   vmlinux download URL      (default: pinned Firecracker CI build)
   FC_ROOTFS       rootfs.ext4 path
   FC_VCPUS        vCPUs per VM              (default: 1)
   FC_MEM_MIB      MiB per VM                (default: 128)