Update broken link in top-level README
Update broken link in top-level README

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