message: Make more like a table of contents
diff: Before sending your pull requests, make sure you followed this list.
  -- [ ] Read [contributing guidelines](CONTRIBUTING.md).
  -- [ ] Read [Code of Conduct](CODE_OF_CONDUCT.md).
  -- [ ] Ensure you have signed the [Contributor License Agreement (CLA)](https://cla.developers.google.com/).
  -- [ ] Check if my changes are consistent with the [guidelines](https://github.com/tensorflow/tensorflow/blob/master/CONTRIBUTING.md#general-guidelines-and-philosophy-for-contribution).
  -- [ ] Changes are consistent with the [Coding Style](https://github.com/tensorflow/tensorflow/blob/master/CONTRIBUTING.md#c-coding-style).
  -- [ ] Run [Unit Tests](https://github.com/tensorflow/tensorflow/blob/master/CONTRIBUTING.md#running-unit-tests).
  +- Read [contributing guidelines](CONTRIBUTING.md).
  +- Read [Code of Conduct](CODE_OF_CONDUCT.md).
  +- Ensure you have signed the [Contributor License Agreement (CLA)](https://cla.developers.google.com/).
  +- Check if my changes are consistent with the [guidelines](https://github.com/tensorflow/tensorflow/blob/master/CONTRIBUTING.md#general-guidelines-and-philosophy-for-contribution).
  +- Changes are consistent with the [Coding Style](https://github.com/tensorflow/tensorflow/blob/master/CONTRIBUTING.md#c-coding-style).
  +- Run [Unit Tests](https://github.com/tensorflow/tensorflow/blob/master/CONTRIBUTING.md#running-unit-tests).
  ## How to become a contributor and submit your own code
  