Add ROOT import to filterHEPMC3.py (#247)

Author: wdconinc

benchmarks/lowq2_reconstruction/filterHEPMC3.py

@@ -1,4 +1,4 @@
-
+import ROOT  # noqa: F401; loads core libraries required by pyhepmc3
 from pyHepMC3 import HepMC3 as hm
 from pyHepMC3.rootIO import HepMC3 as hmrootIO
 import argparse
@@ -41,4 +41,4 @@
 
 reader.close()
 writer.close()
-print(f"Filtered file written to {output_file}")
+print(f"Filtered file written to {output_file}")