GENIE installation instructions

For updated (2020) version of installation instructions for GENIE and it’s prerequisites, see:

https://www.overleaf.com/read/ypgqrtssmnxp

This is an updated version of original GENIE installation instructions: https://hep.ph.liv.ac.uk/~costasa/genie/get_started.html. In the updated version a fork from GENIE is used to install GENIE Generator with modified gevegn application, which allowes to save overall (file-vise) normalization. Note that while this modification will not interfere with standard simulation, it is no longer required by genie-reader project.