docs/system/bootindex: Make it clear that s390x can also boot from virtio-net

Let's make it clear that s390x can also boot from virtio-net, to avoid
that people think that s390x can only boot from disk devices.

Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Message-ID: <20241111105506.264640-1-thuth@redhat.com>
Reviewed-by: Prasad Pandit <pjp@fedoraproject.org>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

docs/system/bootindex.rst

@@ -53,7 +53,7 @@ booting.  For instance, the x86 PC BIOS boot specification allows only one
 disk to be bootable.  If boot from disk fails for some reason, the x86 BIOS
 won't retry booting from other disk.  It can still try to boot from
 floppy or net, though. In the case of s390x BIOS, the BIOS will try up to
-8 total devices, any number of which may be disks.
+8 total devices, any number of which may be disks or virtio-net devices.
 
 Sometimes, firmware cannot map the device path QEMU wants firmware to
 boot from to a boot method.  It doesn't happen for devices the firmware