Update README.md

Author: HaoUNSW

README.md

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 # PISA
 
+## Introduction
+This repository is the reporisity of **Prompt-Based Time Series Forecasting: A New Task and Dataset** (NeurIPS 2022 Datasets and Benchmarks Track, currently under submission). PISA is a large-scale dataset including three real-world forecasting scenarios (three sub-sets) with 311,932 data instances in total. It is designed to support and facilitate the novel PromptCast task proposed in the paper. 
+
 ## Updates
 
 ***2022/06/10***