Add pass description in GenHPVM.h

hpvm/include/GenHPVM/GenHPVM.h

-//== GenHPVM.h - Header file for "LLVM IR to HPVM IR Pass" =//
+//==------- GenHPVM.h - Header file for "LLVM IR to HPVM IR Pass" ----------==//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -6,6 +6,13 @@
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+//
+// This file defines the GenHPVM pass responsible for converting HPVM-C to 
+// HPVM intrinsics. Note that this pass relies on memory-to-register optimiza-
+// tion pass to execute before this executes. 
+//
+//===----------------------------------------------------------------------===//
+ 
 
 #include "SupportHPVM/HPVMTimer.h"
 #include "llvm/IR/DerivedTypes.h"