Add Radio Fresnel tool for modeling (#48)

Add the Radio Fresnel tool as an example path modeling tool for Network 
Design.

arednNetworkDesign/network_modeling.rst

@@ -66,6 +66,21 @@ Simply click on the map at the bottom of the webpage to add an endpoint for each
 
 ----
 
+Radio Fresnel Tool
+++++++++++++++++++
+
+This web-based tool will generate a KML file which can be viewed as a 3D path profile using *Google Earth* software. Radio Fresnel is available here: http://www.radiofresnel.com
+
+Simply enter the required site information into the online form and click the *Get KML* button at the bottom of the webpage. There is a sample KML file as well as a video tutorial for how to use the tool.
+
+----
+
+.. image:: _images/radiofresnel.png
+   :alt: Radio Fresnel Tool
+   :align: center
+
+----
+
 Determining Node or Network Coverage
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