[CI:DOC] Add linger to troubleshooting

Adding a troubleshooting note about how to configure systemd
to linger for detached containers in rootless mode.  This came
up in an email stream on the Podman mailing list today and
answered by @mheon

Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>

troubleshooting.md

@@ -517,3 +517,23 @@ The runtime uses `setgroups(2)` hence the process looses all additional groups
 the non-root user has. If you use the `crun` runtime, 0.10.4 or newer,
 then you can enable a workaround by adding `--annotation io.crun.keep_original_groups=1`
 to the `podman` command line.
+
+### 22) A rootless container running in detached mode is closed at logout
+
+When running a container with a command like `podman run --detach httpd` as
+a rootless user, the container is closed upon logout and is not kept running.
+
+#### Symptom
+
+When logging out of a rootless user session, all containers that were started
+in detached mode are stopped and are not kept running.  As the root user, these
+same containers would survive the logout and continue running.
+
+#### Solution
+
+When systemd notes that a session that started a Podman container has exited,
+it will also stop any containers that has been associated with it.  To avoid
+this, use the following command before logging out: `loginctl enable-linger`.
+To later revert the linger functionality, use `loginctl disable-linger`.
+
+LOGINCTL(1), SYSTEMD(1)