qemu-options.hx: Document missing -drive options

They are 'werror', 'rerror' and 'readonly'.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

qemu-options.hx

@@ -160,6 +160,14 @@ an untrusted format header.
 This option specifies the serial number to assign to the device.
 @item addr=@var{addr}
 Specify the controller's PCI address (if=virtio only).
+@item werror=@var{action},rerror=@var{action}
+Specify which @var{action} to take on write and read errors. Valid actions are:
+"ignore" (ignore the error and try to continue), "stop" (pause QEMU),
+"report" (report the error to the guest), "enospc" (pause QEMU only if the
+host disk is full; report the error to the guest otherwise).
+The default setting is @option{werror=enospc} and @option{rerror=report}.
+@item readonly
+Open drive @option{file} as read-only. Guest write attempts will fail.
 @end table
 
 By default, writethrough caching is used for all block device.  This means that