Update README.md

tutorials/image/cifar10/README.md

-**NOTE: We recommend looking at the newer [cifar10_estimator](https://github.com/tensorflow/models/tree/master/tutorials/image/cifar10_estimator) example instead.**
+**NOTE: For users interested in multi-GPU, we recommend looking at the newer [cifar10_estimator](https://github.com/tensorflow/models/tree/master/tutorials/image/cifar10_estimator) example instead.**
 
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