Create readme.txt

benchmarks/material_budget/readme.txt

+This code is based on root and framework independent and can be used to extract the material budget using the root geometry of the ePIC tracker.  
+Shyam Kumar; shyam.kumar@ba.infn.it; shyam055119@gmail.com
+Steps:
+1. put the root geometry file in the same directory
+2. Replace the geometry root file name in the code 
+run using the command root -l PlotMaterialBudget_ePIC.C