Update README.md

Added reference to IEEE S&T journal paper

Author: jfabini

README.md

@@ -6,4 +6,6 @@ go-flows
 This is a highy customizable general-purpose flow exporter. For more
 information have a look at [godoc](https://godoc.org/github.com/CN-TU/go-flows).
 
-This flow exporter implementation will be featured in an upcoming journal publication. As soon as it is published, we will replace this information with the citation. Please use this citation, if available.
+This flow exporter implementation is featured along with a comparison against other flow exporters and related performance measurements in the [IEEE Surveys & Tutorials journal article cited below](https://ieeexplore.ieee.org/document/9076310). Please use this citation whenever using or referencing go-flows:
+
+G. Vormayr, J. Fabini and T. Zseby, "Why are My Flows Different? A Tutorial on Flow Exporters," in IEEE Communications Surveys & Tutorials, vol. 22, no. 3, pp. 2064-2103, thirdquarter 2020, doi: 10.1109/COMST.2020.2989695.