Documentation suggestion: run example commands when creating the documentation

[eriksjolund]

If the example commands were run as part of the documentation generation, the command output would always stay up to date.

An example of incorrect output:
https://docs.podman.io/en/latest/markdown/podman-generate-systemd.1.html#generate-systemd-unit-file-for-a-container-with-new-flag
Although --files is given as option to the command
sudo podman generate systemd --new --files --name bb310a0780ae
the example shows output.