message: Update README.md for build instructions
diff: @@ -7,7 +7,7 @@ available in TensorFlow's built-in support.
  The TensorFlow I/O package (`tensorflow-io`) could be built from source:
  ```sh
  -$ docker run -it tensorflow/tensorflow:custom-op /bin/bash
  +$ docker run -it -v ${PWD}:/working_dir -w /working_dir tensorflow/tensorflow:custom-op
  $ # In docker
  $ ./configure.sh
  $ bazel build build_pip_pkg
  