Update README.md

Author: we1pingyu

README.md

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 # Consistency-basd Active Learning for Object Detection
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+## Introduction
+This repo is the official implementation CALD: [**Consistency-basd Active Learning for Object Detection.**](https://arxiv.org/abs/2103.10374)
+
 ## Requirement
 - pytorch>=1.7.1
 - torch=0.8.2