addition to README

Hi,

In the interest of transparency, and preventing people getting confused, I would request that the following is added to the README:

For the Users of ROOT, the equivalent functionality can be accomplished without additional packages in a bare ROOT6 session as follows.

import ROOT
jppd = '/pbs/throng/km3net/src/Jpp/master/software'
ROOT.gInterpreter.AddIncludePath( jppd )
ROOT.gInterpreter.ProcessLine('#include "'+jppd+'/JPhysics/JPDF_t.hh"')

pdf = ROOT.JShowerPDF_t("/pbs/throng/km3net/src/Jpp/v12.1.0/data/J%p.dat", 1.5 )

result = pdf.calculate(1000, 100, 0.5, 0.1, 0.1 , 100 )
print ( result.f, result.V )

btw: Tom: do you see warning when compiling JPDF_t.hh with clang?