Fix F1 score formula in pr-curves README.md (#984)
Fix F1 score formula in pr-curves README.md (#984)

Fixes #980.
tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard