update site dox - windows prefer msvs-ninja and add vulkan

site/user/quick/windows.md

 Windows
 =======
 
 Prerequisites
 -------------
 
 Make sure the following have been installed:
 
 *   [Visual C++ 2013 Express or later, available for
     free](https://www.visualstudio.com/downloads/download-visual-studio-vs#d-express-windows-8)
@@ skipping 39 matching lines @@
 We use the open-source Gyp tool to generate Visual Studio projects (and
 analogous build scripts on other platforms) from our multi-platform "gyp"
 files.
 
 Three Gyp generators are used on Windows:
 
 *   `ninja` - Run ninja yourself, without VisualStudio  project files,
 
 *   `msvs-ninja` - Develop from a fully-integrated Visual Studio.
     Gyp generates Visual-Studio-compatible project files that still
-    ultimately build using ninja
+    ultimately build using ninja. This is the preferred and better maintained
+    way of using Visual Studio.
 
-*   `msvs` - Use Visual Studio's own (slower) build system
+*   `msvs` - Use Visual Studio's own (slower) build system. This is not as well
+     maintained as msvs-ninja. The msvs and ninja output can clobber each other
+     so building from both the command line and Visual Studio can produce bad
+     states that can be fixed by deleting the out directory and rerunning
+     gyp_skia.
 
 To choose which ones to use, set the `GYP_GENERATORS` environment
 variable to a comma-delimited list of generators before running
 sync-and-gyp. The default value for `GYP_GENERATORS` is
 `ninja,msvs-ninja`.  For example to enable the `ninja` and `msvs`
 generators:
 
 <a name="env"></a>Setting Enviroment Variables in Windows CMD.EXE
 -----------------------------------------------------------------
 
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     click on "Yes" to rebuild it.
 
 6.  Once the build is complete, you should see a window with various
     example graphics. To move through the sample app, use the
     following keypresses:
     -    right- and left-arrow key: cycle through different test pages
     -    'D' key: cycle through rendering methods for each test page
     -    other keys are defined in SampleApp.cpp’s
          SampleWindow::onHandleKey() and SampleWindow::onHandleChar()
          methods