[Papers] Update papers using DGL (dmlc#2459)

Added three papers using DGL:
NHK_STRL at WNUT-2020 Task 2: GATs with Syntactic Dependencies as Edges and CTC-based Loss for Text Classification
Relation-aware Graph Attention Networks with Relational Position Encodings for Emotion Recognition in Conversations
PGM-Explainer: Probabilistic Graphical Model Explanations for Graph Neural Networks

README.md

@@ -269,6 +269,12 @@ We are currently in Beta stage.  More features and improvements are coming.
 
 1. [**Computing Graph Neural Networks: A Survey from Algorithms to Accelerators**](https://arxiv.org/pdf/2010.00130.pdf), *Sergi Abadal, Akshay Jain, Robert Guirado, Jorge López-Alonso, Eduard Alarcón*
 
+1. [**NHK_STRL at WNUT-2020 Task 2: GATs with Syntactic Dependencies as Edges and CTC-based Loss for Text Classification**](https://www.aclweb.org/anthology/2020.wnut-1.43.pdf), *Yuki Yasuda, Taichi Ishiwatari, Taro Miyazaki, Jun Goto*
+
+1. [**Relation-aware Graph Attention Networks with Relational Position Encodings for Emotion Recognition in Conversations**](https://www.aclweb.org/anthology/2020.emnlp-main.597.pdf), *Taichi Ishiwatari, Yuki Yasuda, Taro Miyazaki, Jun Goto*
+
+1. [**PGM-Explainer: Probabilistic Graphical Model Explanations for Graph Neural Networks**](https://proceedings.neurips.cc/paper/2020/file/8fb134f258b1f7865a6ab2d935a897c9-Paper.pdf), *Minh N. Vu, My T. Thai*
+
 
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