[#1] Add dependency on coreutils

`jirac` now needs `gtac` to run.
Read https://github.com/jirac/jirac/issues/30 for info.
Remove git dependency

It is a bad idea to depends on git since brew allow the usage
of non-homebrew git.
Installing Jirac should not install git from brew formula if the
user use another git installation method.
Remove trailing whitespace
Document the way to upgrade jirac with brew