Document how to select build configuration with Visual C++ IDE or command line.

llvm-svn: 210273
diff --git a/llvm/docs/GettingStartedVS.rst b/llvm/docs/GettingStartedVS.rst
index aa980d2..d914cc1 100644
--- a/llvm/docs/GettingStartedVS.rst
+++ b/llvm/docs/GettingStartedVS.rst
@@ -99,6 +99,9 @@
      build.
    * See the :doc:`LLVM CMake guide <CMake>` for detailed information about
      how to configure the LLVM build.
+   * CMake generates project files for all build types. To select a specific
+     build type, use the Configuration manager from the VS IDE or the 
+     ``/property:Configuration`` command line option when using MSBuild.
 
 6. Start Visual Studio