Fix arxiv link

README.md

 # LOST 
 Pytorch implementation of the unsupervised object discovery method **LOST**. More details can be found in the paper:
 
-**Localizing Objects with Self-Supervised Transformers and no Labels** [[arXiv](https://arxiv.org/abs/)]  
+**Localizing Objects with Self-Supervised Transformers and no Labels** [[arXiv](https://arxiv.org/abs/2109.14279)]  
 by *Oriane Siméoni, Gilles Puy, Huy V. Vo, Simon Roburin, Spyros Gidaris, Andrei Bursuc, Patrick Pérez, Renaud Marlet and Jean Ponce*
 
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