README inaccurately says it's chainer bindings

[ezyang]

If I understand recent correspondence correctly, ideep will be the official frontend for mkl-dnn, not just for chainer. README should be updated.

[gujinghui]

@ezyang
the mkldnn-bridge for pytorch/caffe2 is being separate from ideep chainer.
we're reducing the LOC and improving the API only for pytorch/caffe2.
when done, we plan to make the mkldnn-bridge as a part of pytorch/caffe2, instead of a submodule.