Added information on how to reference gprMax in publications.

README.rst

@@ -12,6 +12,13 @@ gprMax is released under the GNU General Public License v3 or higher (http://www
 
 gprMax is written in Python 3 (https://www.python.org) and includes performance-critical parts written in Cython/OpenMP (http://cython.org).
 
+Cite gprMax
+-----------
+
+If you use gprMax and publish your work we would be grateful if you could cite gprMax using the following references:
+
+* Warren, C., Giannopoulos, A., & Giannakis I. (2015). An advanced GPR modelling framework – the next generation of gprMax, In `Proc. 8th Int. Workshop Advanced Ground Penetrating Radar`
+* Giannopoulos, A. (2005). Modelling ground penetrating radar by GprMax, `Construction and Building Materials`, 19(10), 755-762. doi:10.1016/j.conbuildmat.2005.06.007
 
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