4ti2 installation guide for MacOSX machines

Create a directory for 4ti2, call it '4ti2', say. Download the file for MacOSX machines to the new directory '4ti2'. Go to directory '4ti2'. Unzip file '4ti2_v1.2_macOSX.tgz'. Remove file '4ti2_v1.2_macOSX.tgz'.