[Beignet] [PATCH v3 4/4] Add document of video motion estimation support.

[Song, Ruiling]

Just find two typos.

> +++ b/docs/howto/video-motion-estimation-howto.mdwn
> @@ -0,0 +1,79 @@
> +Video Motion Vector HowTo
> +==========================
> +
> +Beignet now supports cl_intel_accelerator and part of
> +cl_intel_motion_estimation, which are Khronos officail extensions. It
                                                                                     Typo:   official
> +provides a hardware acceleration of video motion vector to users.
> +
> +Supported hardware platfrom and limitation
                                Typo:  platform

Thanks!
Ruiling