docs: generate systemd: XDG_RUNTIME_DIR
A conversation on the customer portal suggests that to add an extra note
about the requirement of XDG_RUNTIME_DIR to be set.
@@ -10,7 +10,7 @@ podman\-generate\-systemd - Generate systemd unit file(s) for a container or pod
**podman generate systemd** will create a systemd unit file that can be used to control a container or pod.
By default, the command will print the content of the unit files to stdout.
-_Note: If you use this command with the remote client, you would still have to place the generated units on the remote system._
+_Note: If you use this command with the remote client, you would still have to place the generated units on the remote system. Moreover, please make sure that the XDG_RUNTIME_DIR environment variable is set. If unset, you may set it via `export XDG_RUNTIME_DIR=/run/user/$(id -u)`._
## OPTIONS
