Update LICENSE

LICENSE

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+                          PUBLIC DOMAIN NOTICE
+              National Center for Biotechnology Information
+
+This software/database is a "United States Government Work" under the terms of
+the United States Copyright Act.  It was written as part of the author's
+official duties as a United States Government employee and thus cannot be
+copyrighted.  This software/database is freely available to the public for use.
+The National Library of Medicine and the U.S. Government have not placed any
+restriction on its use or reproduction.
+
+Although all reasonable efforts have been taken to ensure the accuracy and
+reliability of the software and data, the NLM and the U.S. Government do not and
+cannot warrant the performance or results that may be obtained by using this
+software or data. The NLM and the U.S. Government disclaim all warranties,
+express or implied, including warranties of performance, merchantability or
+fitness for any particular purpose.
+
+Please cite the author in any work or product based on this material:
+Qiao Jin, Won Kim, Qingyu Chen, Donald C Comeau, Lana Yeganova, John Wilbur, Zhiyong Lu.
+MedCPT: Contrastive Pre-trained Transformers with Large-scale PubMed Search Logs for Zero-shot Biomedical Information Retrieval