[FEAT] Change the doc for rootless docker users

[Dawnowl444]

Is this a new feature request?

• I have searched the existing issues

Wanted change

Update the documentation/readme for people using docker in rootless mode.
https://docs.docker.com/engine/security/rootless/

Reason for change

The actual documentation says to use PUID and PGID according to the main user, but, when using rootless docker the docker root user is the main user and abc will be an unkown user on the parent filesystem.

Post that made me understand that issue itzg/docker-minecraft-server#1934 (comment)

Proposed code change

When using rootless docker PUID and PGID must be set to 0

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[thespad]

Please see our [support policy] (https://docs.linuxserver.io/misc/support-policy/)

We don't formally support rootless operation and don't want to confuse users by trying to explain user namespacing in our readme docs. We expect that if people are running rootless environments that they understand what that means and how it changes interactions with the host namespaces when running a container.