Add 1.7.0 relnotes to RELEASE.md (#1080)
Add 1.7.0 relnotes to RELEASE.md (#1080)


tensorflow/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard