osbuild: print the nsenter command needed to get a shell in the container

This is useful for debugging, and would be as a very lightweight ssh
session, but one that only insepcts the environment without hooking
into anything.

osbuild

@@ -69,6 +69,8 @@ def main(pipeline_path, from_archive, save):
 
             print()
             print(f"{RESET}{BOLD}{i}. {name}{RESET} {options_str}")
+            print("Inspect with:")
+            print(f"\t# nsenter -a --wd=/root -t `machinectl show {os.path.basename(root)} -p Leader --value`")
             print()
 
             try: