Update qm manpage to fix install instructions

[aesteve-rh]

Currently installing as instructed in the man at: https://github.com/containers/qm/blob/main/qm.8.md?plain=1#L68
Results in an error:

# dnf install --installroot=/usr/lib/qm/rootfs setools-console
error: cannot open Packages database in /usr/lib/qm/rootfs/var/lib/rpm
Error: Error: rpmdb open failed

Probably since /usr/lib/qm/rootfs is just partial rootfs, and /etc/qm and /var/qm may be needed as well.

Explore the way to handle it and document it properly.

[Yarboa]

@aesteve-rh
Probably this one will do the trick

 dnf install --setopt=reposdir=/etc/qm/yum.repos.d --installroot=/usr/lib/qm/rootfs -y <pkg>

Did you give it a try?

[aesteve-rh]

Did you give it a try?

Yeah, it does not work for me either.