Update readme

* Remove mention of VS2012 support.
* Update WindowsTargetPlatformVersion info for newer version of Premake.

README.md

@@ -14,10 +14,10 @@ The library implements depth of field using a Bartlett and Box filter. There is
 * AMD Radeon™ GCN-based GPU (HD 7000 series or newer)
   * Or other DirectX® 11 compatible discrete GPU with Shader Model 5 support
 * 64-bit Windows® 7 (SP1 with the [Platform Update](https://msdn.microsoft.com/en-us/library/windows/desktop/jj863687.aspx)), Windows® 8.1, or Windows® 10
-* Visual Studio® 2012, Visual Studio® 2013, or Visual Studio® 2015
+* Visual Studio® 2013 or Visual Studio® 2015
 
 ### Getting started
-* Visual Studio solutions for VS2012, VS2013, and VS2015 can be found in the `amd_depthoffieldfx_sample\build` directory.
+* Visual Studio solutions for VS2013 and VS2015 can be found in the `amd_depthoffieldfx_sample\build` directory.
 * There are also solutions for just the core library in the `amd_depthoffieldfx\build` directory.
 * Additional documentation is available in the `amd_depthoffieldfx\doc` directory.
 
@@ -26,9 +26,9 @@ The Visual Studio solutions and projects in this repo were generated with Premak
 
 This version of Premake has been modified from the stock version to use the property sheet technique for the Windows SDK from this [Visual C++ Team blog post](http://blogs.msdn.com/b/vcblog/archive/2012/11/23/using-the-windows-8-sdk-with-visual-studio-2010-configuring-multiple-projects.aspx). The technique was originally described for using the Windows 8.0 SDK with Visual Studio 2010, but it applies more generally to using newer versions of the Windows SDK with older versions of Visual Studio.
 
-The default SDK for a particular version of Visual Studio (for 2012 or higher) is installed as part of Visual Studio installation. This default (Windows 8.0 SDK for Visual Studio 2012 and Windows 8.1 SDK for Visual Studio 2013) will be used if newer SDKs do not exist on the user's machine. However, the projects generated with this version of Premake will use the next higher SDK (Windows 8.1 SDK for Visual Studio 2012 and Windows 10 SDK with Visual Studio 2013), if the newer SDKs exist on the user's machine.
+By default, Visual Studio 2013 projects will compile against the Windows 8.1 SDK. However, the VS2013 projects generated with this version of Premake will use the next higher SDK (i.e. the Windows 10 SDK), if the newer SDK exists on the user's machine.
 
-For Visual Studio 2015, this version of Premake adds the `WindowsTargetPlatformVersion` element to the project file to specify which version of the Windows SDK will be used. To change `WindowsTargetPlatformVersion` for Visual Studio 2015, change the value for `_AMD_WIN_SDK_VERSION` in `premake\amd_premake_util.lua` and regenerate the Visual Studio files.
+For Visual Studio 2015, the `systemversion` Premake function is used to add the `WindowsTargetPlatformVersion` element to the project file, to specify which version of the Windows SDK will be used. To change `WindowsTargetPlatformVersion` for Visual Studio 2015, change the value for `_AMD_WIN_SDK_VERSION` in `premake\amd_premake_util.lua` and regenerate the Visual Studio files.
 
 ### Third-Party Software
 * DXUT is distributed under the terms of the MIT License. See `framework\d3d11\dxut\MIT.txt`.