QEMU cheatsheet: partx nbd0

[KevinRSX]

https://wangziqi2013.github.io/article/2022/03/09/qemu-cheat-sheet.html
If the existence of /dev/nbd0 is not known to the partition table, users need to sudo partx -a /dev/nbd0 to add that entry. That should be done after mkfs and before mount /dev/nbd0. Otherwise they will get some errors like mount: <path>: special device /dev/nbd0/ does not exist (a path prefix is not a directory).