message: Center-align the logo image and set size
diff: XLA (Accelerated Linear Algebra) is a domain-specific compiler for linear
  algebra that optimizes TensorFlow computations.
  -![XLA logo](xlalogo.png)
  +<p align="center">
  + <img width="200" src="xlalogo.png"/>
  +</p>
  See the [documentation](https://www.tensorflow.org/performance/xla/) for more
  details.
  