[CI:DOCS]rootless exec cannot join root namespace
add a quick note in the rootless.md about usage of --net=host as rootless and subsequent podman execs.
Fixes:
@@ -44,3 +44,4 @@ can easily fail
* If a build is attempting to use a UID that is not mapped into the user namespace mapping for a container, then builds will not be able to put the UID in an image.
* Making device nodes within a container fails, even when running --privileged.
* The kernel does not allow non root user processes (processes without CAP_MKNOD) to create device nodes. If a container needs to create device nodes, it must be run as root.
+* When using --net=host with rootless containers, subsequent podman execs to that container will not join the host network namespace because it is owned by root.
