message: Add an example to tf.math.sign docstring.
diff: @@ -5,5 +5,9 @@ op {
  `y = sign(x) = -1` if `x < 0`; 0 if `x == 0`; 1 if `x > 0`.
  For complex numbers, `y = sign(x) = x / |x|` if `x != 0`, otherwise `y = 0`.
  +
  +Example usage:
  +>>> tf.math.sign([0., 2., -3.])
  +<tf.Tensor: id=16, shape=(3,), dtype=float32, numpy=array([ 0., 1., -1.], dtype=float32)>
  END
  }
  