Added link to Iraklis thesis next to Peplinski soil command.

docs/source/input.rst

@@ -316,6 +316,10 @@ Allows you to use a mixing model for soils proposed by Peplinski (http://dx.doi.
 
 For example for a soil with sand fraction 0.5, clay fraction 0.5, bulk density :math:`2~g/cm^3`, sand particle density of :math:`2.66~g/cm^3`, and a volumetric water fraction range of 0.001 - 0.25 use: ``#soil_peplinski: 0.5 0.5 2.0 2.66 0.001 0.25 my_soil``.
 
+.. note::
+
+    Further information on the Peplinski soil model and our implementation can be found in 'Giannakis, I. (2016). Realistic numerical modelling of Ground Penetrating Radar for landmine detection. The University of Edinburgh. (http://hdl.handle.net/1842/20449)'
+
 Object construction commands
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