Document Supported and Tested Versions of Dependencies, Update Example.

This addresses Issue #147. A list of tested versions for each dependency has
been added based on the configurations of the nightly test builds.
The partial example code in the README has been completed and tested
to generate correct output.

README.md

@@ -65,6 +65,7 @@ VTK-m Requires:
   + [CMake](http://www.cmake.org/download/)
       + CMake 3.3+ (for any build)
       + CMake 3.9+ (for CUDA build)
+      + CMake 3.11+ (for Visual Studio generator)
 
 Optional dependencies are:
 
@@ -91,6 +92,21 @@ Optional dependencies are:
       + [OS Mesa](https://www.mesa3d.org/osmesa.html)
       + EGL Driver
 
+VTK-m has been tested on the following configurations:
+  + On Linux 
+      + GCC 4.8.5, 5.4.0, 6.4.0, Clang 3.8.0
+      + CMake 3.9.2, 3.9.3, 3.10.3
+      + CUDA 8.0.61, 9.1.85
+      + TBB 4.4 U2, 2017 U7
+  + On Windows
+      + Visual Studio 2015, 2017
+      + CMake 3.3, 3.11.1
+      + CUDA 9.1.85
+      + TBB 2017 U3, 2018 U2
+  + On MacOS
+      + AppleClang 6.0
+      + TBB 2017 U6
+
 
 ## Building ##
 
@@ -124,14 +140,17 @@ Marching Cubes algorithm on it, and render the results to an image:
 
 ```cpp
 vtkm::io::reader::VTKDataSetReader reader("path/to/vtk_image_file");
-inputData = reader.ReadDataSet();
+vtkm::cont::DataSet inputData = reader.ReadDataSet();
+std::string fieldName = "scalars";
 
-vtkm::Float64 isovalue = 100.0f;
-std::string fieldName = "pointvar";
+vtkm::Range range;
+inputData.GetPointField(fieldName).GetRange(&range);
+vtkm::Float64 isovalue = range.Center();
 
 // Create an isosurface filter
 vtkm::filter::MarchingCubes filter;
 filter.SetIsoValue(0, isovalue);
+filter.SetActiveField(fieldName);
 vtkm::cont::DataSet outputData = filter.Execute(inputData);
 
 // compute the bounds and extends of the input data