message: Fix markdown nit
  Without a leading blank line, it doesn't render properly in
diff: @@ -62,6 +62,7 @@ them. For this reason TensorFlow provides **collections**, which are named lists
  of tensors or other objects, such as `tf.Variable` instances.
  By default every `tf.Variable` gets placed in the following two collections:
  +
  * `tf.GraphKeys.GLOBAL_VARIABLES` --- variables that can be shared across
  multiple devices,
  * `tf.GraphKeys.TRAINABLE_VARIABLES` --- variables for which TensorFlow will
  