message: Clarified difference between FIFOQueue and StagingArea
  * Update performance_models.md
  Clarified that StagingArea doesn't guarantee ordered delivery, contrasting tf.FIFOQueue
  * Add a space.
diff: @@ -29,12 +29,12 @@ implementation is made up of 3 stages:
  The dominant part of each stage is executed in parallel with the other stages
  using `data_flow_ops.StagingArea`. `StagingArea` is a queue-like operator
  -similar to @{tf.FIFOQueue}. The difference is that `StagingArea` offers simpler
  -functionality and can be executed on both CPU and GPU in parallel with other
  -stages. Breaking the input pipeline into 3 stages that operate independently in
  -parallel is scalable and takes full advantage of large multi-core environments.
  -The rest of this section details the stages followed by details about using
  -`data_flow_ops.StagingArea`.
  +similar to @{tf.FIFOQueue}. The difference is that `StagingArea` does not
  +guarantee FIFO ordering, but offers simpler functionality and can be executed
  +on both CPU and GPU in parallel with other stages. Breaking the input pipeline
  +into 3 stages that operate independently in parallel is scalable and takes full
  +advantage of large multi-core environments. The rest of this section details
  +the stages followed by details about using `data_flow_ops.StagingArea`.
  ### Parallelize I/O Reads
  