docs: add warning about virt-qemu-run being experimental

We currently note that the QEMU embedded driver is experimental
in the drvqemu.html file, but we should do the same in the
virt-qemu-run man page.
Reviewed-by: NErik Skultety <eskultet@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/manpages/virt-qemu-run.rst

@@ -33,6 +33,11 @@ If the virt-qemu-run program is interrupted (eg Ctrl-C) it will
 immediately terminate the virtual machine without giving the guest
 OS any opportunity to gracefully shutdown.
 
+**NOTE: this tool is currently considered experimental.** Its
+usage and behaviour is still subject to change in future libvirt
+releases. For further information on its usage consult the
+`QEMU driver documentation <https://libvirt.org/drvqemu.html#uriembedded>`_.
+
 OPTIONS
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