Added description for header DFG2LLVM.h

hpvm/include/SupportHPVM/DFG2LLVM.h

@@ -9,6 +9,11 @@
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+//
+// This defines different classes for traversing Dataflow Graph for code 
+// generation for different nodes for different targets.
+//
+//===----------------------------------------------------------------------===//
 
 #include "BuildDFG/BuildDFG.h"
 #include "SupportHPVM/HPVMHint.h"