Fix code formatting example in README (#602)
Fix code formatting example in README (#602)

Specified that a code snippet is bash.
tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,francoisluus/tensorboard-supervise,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,francoisluus/tensorboard-supervise,francoisluus/tensorboard-supervise,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard