Change installing from source to installing from nightly build

tutorials/README.md

 # Tutorial Models
 
-This repository contains models referenced to from the [TensorFlow tutorials](https://www.tensorflow.org/tutorials/). We recommend [installing TensorFlow from source](https://www.tensorflow.org/get_started/os_setup#installing_from_sources) using the current master version rather than the r0.12 release before running these models.
+This repository contains models referenced to from the [TensorFlow tutorials](https://www.tensorflow.org/tutorials/). We recommend installing TensorFlow from the [nightly builds](https://github.com/tensorflow/tensorflow#installation) rather than the r0.12 release before running these models.