Update top-level EGSnrc README
Update top-level EGSnrc README

nrc-cnrc/EGSnrc,marenaud/EGSnrc,crcrewso/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,mchamberland/EGSnrc,MartinMartinov/EGSnrc,crcrewso/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,ftessier/EGSnrc,mchamberland/EGSnrc,MartinMartinov/EGSnrc,marenaud/EGSnrc,crcrewso/EGSnrc,crcrewso/EGSnrc,ftessier/EGSnrc,crcrewso/EGSnrc,marenaud/EGSnrc,MartinMartinov/EGSnrc,MartinMartinov/EGSnrc,mchamberland/EGSnrc,ftessier/EGSnrc,marenaud/EGSnrc,marenaud/EGSnrc,ftessier/EGSnrc,MartinMartinov/EGSnrc,marenaud/EGSnrc,ftessier/EGSnrc,nrc-cnrc/EGSnrc,mchamberland/EGSnrc,nrc-cnrc/EGSnrc,ftessier/EGSnrc