Add reference to README.md

README.md

@@ -10,3 +10,6 @@ The entire data, including the intervals in-between the photoelectron peaks, are
 To get started, have a look at ```example.py```.
 
 
+## References
+
+Jack Rolph, Erika Garutti, Robert Klanner, Tobias Quadfasel, Jörn Schwandt: _PeakOTron: A Python module for fitting charge spectra of Silicon Photomultipliers_.  [doi.org/10.1016/j.nima.2023.168544](https://doi.org/10.1016/j.nima.2023.168544)
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