Adding a new UserHook to compute the DJRs for CKKW_L merging scheme and the tutorial about the use of the UserHook
I Added a new UserHook for Pythia8 to compute the DJRs for the CKKW_L merging algorithm. Furthermore, in the Pythia8_i README, I integrated a tutorial providing a detailed explanation of the steps for using the UserHook and interpreting the resulting histograms.