Update mc.MGPy8EG_Wtaunu_FxFx_3jets.py for leptonic decays ONLY

Francesco Giulirequested to merge
fgiuli-master-patch-73774 into master

I added the following lines to the Wtaunu FxFx JOs to allow taus to decay only to leptons:

#tau decay to electron or muons ONLY
genSeq.Pythia8.Commands += [ "15:onMode = off", "15:onIfAny = 11 13" ]

Merge request reports