Added info on MSVS and nvcc paths.

README.rst

@@ -117,6 +117,8 @@ Microsoft Windows
 
 * Download and install `Microsoft Visual C++ 2015 Build Tools <http://download.microsoft.com/download/5/F/7/5F7ACAEB-8363-451F-9425-68A90F98B238/visualcppbuildtools_full.exe>`_ (currently you must use the 2015 version, not 2017). Use the custom installation option and deselect everything apart from the Windows SDK for your version of Windows.
 
+If you have problems with building gprMax you may need to add Microsoft Visual Studio tools to your path environment variable, usually :code:`C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin`
+
 Alternatively if you are using Windows 10 and feeling adventurous you can install the `Windows Subsystem for Linux <https://msdn.microsoft.com/en-gb/commandline/wsl/about>`_ and then follow the Linux install instructions for gprMax. Note however that currently WSL does not aim to support GUI desktops or applications, e.g. Gnome, KDE, etc....
 
 3. Build and install gprMax