message: add usage examples/doctests
diff: @@ -1926,6 +1926,17 @@ def is_non_decreasing(x, name=None):
  See also: `is_strictly_increasing`
  + ```python
  + >>> x1 = tf.constant([1.0, 1.0, 3.0])
  + >>> tf.print(tf.math.is_non_decreasing(x1))
  + 1
  +
  + >>> x2 = tf.constant([3.0, 1.0, 2.0])
  + >>> tf.print(tf.math.is_non_decreasing(x1))
  + 0
  +
  + ```
  +
  Args:
  x: Numeric `Tensor`.
  name: A name for this operation (optional). Defaults to "is_non_decreasing"
  @@ -1960,6 +1971,17 @@ def is_strictly_increasing(x, name=None):
  See also: `is_non_decreasing`
  + ```python
  + >>> x1 = tf.constant([1.0, 2.0, 3.0])
  + >>> tf.print(tf.math.is_strictly_increasing(x1))
  + 1
  +
  + >>> x2 = tf.constant([3.0, 1.0, 2.0])
  + >>> tf.print(tf.math.is_strictly_increasing(x1))
  + 0
  +
  + ```
  +
  Args:
  x: Numeric `Tensor`.
  name: A name for this operation (optional).
  