adding suggested comment

Author: joaosaffran

llvm/include/llvm/MC/DXContainerRootSignature.h

@@ -74,6 +74,7 @@ struct StaticSampler {
   uint32_t ShaderRegister;
   uint32_t RegisterSpace;
   dxbc::ShaderVisibility ShaderVisibility;
+  // Version 3 onwards:
   uint32_t Flags;
 };