Update README.md

Author: PauloCarvalhoRJ

README.md

@@ -5,9 +5,11 @@ Repository of the GammaRay geostatistics software.
 
 Abstract:
 GammaRay is a graphical user interface (GUI) that automates geostatistical workflows by driving and coordinating the several modules of the renowned Geostatistical Software Library (GSLib).  The main purpose of GammaRay is to add a user-friendly interface layer on top of the scientifically and numerically robust GSLib, greatly automating parameter file editing and module chaining so the practitioner can focus on geostatistics.  GammaRay was conceived as a free and portable alternative to WinGSLib®, which is a commercial software available only for Microsoft Windows® users.  GammaRay is also open source and thus is subject to code review and can receive contributions from other software developers as well as user feedback, suggestions and bug reports.  GammaRay is built with the C++ programming language upon the famous Qt library to leverage the construction of a modern and platform independent graphical user interface.<br><br>
-If you enjoyed this project, you might also enjoy GeostatsPy: https://github.com/GeostatsGuy/GeostatsPy and PyLPM: https://pylpm.readthedocs.io/en/latest/<br><br>
+GammaRay can be freely used in personal, academic and commercial applications, provided you give due credit to the authors.  You can cite it as:<br>
+    CARVALHO, P. R. M.; MACHADO, P. L. et al. GammaRay: A graphical interface to GSLib and other geomodeling algorithms, (2014), GitHub repository, https://github.com/PauloCarvalhoRJ/gammaray<br><br>
+If you enjoyed this project, you might also enjoy GeostatsPy: https://github.com/GeostatsGuy/GeostatsPy and PyLPM: https://pylpm.readthedocs.io/en/latest/<br>
 
-Python script to convert Eclipse grids to Paraview-compatible VTU format: https://github.com/BinWang0213/PyGRDECL<br><br>
+Python script to convert Eclipse grids to Paraview-compatible VTU format: https://github.com/BinWang0213/PyGRDECL
 
 VERSION HISTORY:<br>
 &nbsp;&nbsp;&nbsp;Version 6.5   - vertical proportion curves, improvements Automatic Variogram Fitting, enhancements and several fixes.<br>