updated readme

Author: mounika

README.md

@@ -75,6 +75,10 @@ Your CSV file should look like the following:
 
 This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
 
+## Reference
+
+1.	Thakkallapally M, Bradenday J, Aluthge D, Sarkar IN, Crowley KM, Chen E. OMOPVocabMapper: A Tool for Mapping ICD Codes to OMOP Concepts. AMIA 2024 Annual Symposium. [Poster Abstract] - Accepted
+