qemu-options: Add missing newline to -accel help text

qemu-options: Add missing newline to -accel help text

The newline was removed by commit c97d6d2c, and broke -help output:

Before this patch:

  $ qemu-system-x86_64 -help | grep smp
                  thread=single|multi (enable multi-threaded TCG)-smp [...]

After this patch:

  $ qemu-system-x86_64 -help  | grep smp
  -smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,sockets=sockets]

Fixes: c97d6d2cdf97edb4aebe832fdba65d701ad7bcb6
Cc: Sergio Andres Gomez Del Real <[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>
Message-Id: <20180611195607[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>