message: Add Apache License Badge
diff: # TensorFlow I/O
  -[![GitHub CI Status Badge](https://github.com/tensorflow/io/workflows/GitHub%20CI/badge.svg?branch=master)](https://github.com/tensorflow/io/actions?query=branch%3Amaster)
  -[![PyPI Status Badge](https://badge.fury.io/py/tensorflow-io.svg)](https://pypi.org/project/tensorflow-io/)
  -[![CRAN_Status_Badge](https://www.r-pkg.org/badges/version/tfio)](https://cran.r-project.org/package=tfio)
  +[![GitHub CI](https://github.com/tensorflow/io/workflows/GitHub%20CI/badge.svg?branch=master)](https://github.com/tensorflow/io/actions?query=branch%3Amaster)
  +[![PyPI](https://badge.fury.io/py/tensorflow-io.svg)](https://pypi.org/project/tensorflow-io/)
  +[![CRAN](https://www.r-pkg.org/badges/version/tfio)](https://cran.r-project.org/package=tfio)
  +[![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://github.com/tensorflow/io/blob/master/LICENSE)
  [![Documentation](https://img.shields.io/badge/api-reference-blue.svg)](https://www.tensorflow.org/io)
  TensorFlow I/O is a collection of file systems and file formats that are not
  