Merge pull request #10399 from vrothberg/systemd-docs

[CI:DOCS] docs: generate systemd: XDG_RUNTIME_DIR

docs/source/markdown/podman-generate-systemd.1.md

@@ -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