message: Update activations.py
  added usage example for softplus activation
diff: @@ -160,6 +160,14 @@ def selu(x):
  def softplus(x):
  """Softplus activation function.
  + Example Usage:
  +
  + >>> a = tf.constant([-20, -1.0, 0.0, 1.0, 20], dtype = tf.float32)
  + >>> b = tf.keras.activations.softplus(a)
  + >>> b.numpy()
  + [2.0611537e-09, 3.1326166e-01, 6.9314718e-01, 1.3132616e+00, 2.0000000e+01]
  +
  +
  Arguments:
  x: Input tensor.
  