docs: add FAQ entry for subuid/subgid

[bsherman]

Capture of discord chat... should be made into a FAQ entry.

Original concern/question:
I've encountered a bug while rebasing from lxqt-main to vauxite. It seems the permissions get messed up with my distrobox containers and they cannot run! This isn't bad - this is fun! My second issue I've encountered so far with uBlue, but I don't want to file a github issue until I can reproduce it and yield some usable data. When I come home I will attempt to reproduce the bug and post the verbose output from my terminal

My responses:
have you heard of subuid?

I don't think it should change on a rebase, but... my first guess is your subuid (the uid offset used for rootless podman) probably changed...

if you grep $USERNAME /etc/subuid you'll see a number...

It should match the UID of owner for at least some directories under ls -al $HOME/.local/share/containers/storage/volumes

(there's similarly a subgid)

so some of those volumes directories may be owned by your normal uid, but others by the subuid (you, but the rootless, root user)

When i've run into the subuid/subgid problem ( i think when i did a backup/restore of home dir ) I just looked for the subuid/subgid in my .local/share/containers and manually updated my user's values in the /etc/subuid and subgid files. All was better then.