Add documentation about rootless use

[eriksjolund]

I searched for "rootless" in the documentation but didn't find anything:
https://docs.linuxserver.io/?q=rootless

I see that using rootless Podman or rootless Docker is not supported.

containers/podman#15313 (comment)

containers/podman#15313 (comment)

Could you add a note to documentation (https://docs.linuxserver.io)
that using rootless Podman and rootless Docker is not supported?

[sammcj]

Came wondering the same thing!

[raycadle]

I'm using rootless podman to run a few LSIO containers (specifically Nextcloud, Mariadb, and Syncthing) and I've had no container related issues so far. I would be happy to contribute that bit of documentation if it would be of use to the community.

[raycadle]

Created a PR #129, adding documentation around using rootless podman containers.