added div2k to release notes

Author: WilliamHYZhang

docs/release_notes.md

@@ -17,3 +17,5 @@
     [VTAB benchmark](https://arxiv.org/abs/1910.04867).
 *   Add e-SNLI dataset from the paper
     [e-SNLI](http://papers.nips.cc/paper/8163-e-snli-natural-language-inference-with-natural-language-explanations.pdf).
+*	Add DIV2K dataset from the paper
+	[DIV2K](http://www.vision.ee.ethz.ch/~timofter/publications/Agustsson-CVPRW-2017.pdf)