add original pipeline to output

hellpipe/main.py

@@ -5,9 +5,8 @@ import sys
 from . import convert
 
 FILE_START = """\
-# generated with hellpipe
 
-def main():
+def main():\
 """
 FILE_END = """
 if __name__ == "__main__":
@@ -49,6 +48,9 @@ def main():
     for stage in stages:
         print("\n".join(stage.imports))
 
+    print()
+    print("# generated by hellpipe from input pipeline:")
+    print("#", command)
     print(FILE_START)
 
     for stage in stages: