Request to add API documentation for using tf.flags

[NianzuMa]

I saw some tensorflow project contains hyperparameter configuration like:
tf.flags.DEFINE_integer("embedding_dim", 128, "Dimensionality of character embedding (default: 128)")

I think it is better to add corresponding document for using this feature.

[mrry]

Our policy so far has been only to document the features that we intend to support in TensorFlow long-term. Currently we use python-gflags as the implementation for tf.flags, but this is subject to change in future. In the meantime, the documentation for that library is the best source of usage information.

[tobegit3hub]

I'm not sure if TensorFlow will use python-gflags in long-term or not, it would be better to add the link to refer to python-glags's documentation. Anyway, it seems that project has little document, either :(

[bibhu107]

Now Is there any documentation for hyperparameter configuration like?