README: Had wrong paths for Macs/Homebrew
README: Had wrong paths for Macs/Homebrew

ICU in Homebrew has a different path than the previous
documents. In addition, there is now a handy
link: `/usr/local/opt/icu4c`

I updated whole section on ICU to be a little easier for me to
read. Hopefully you approve.
brianmario/charlock_holmes,brianmario/charlock_holmes,brianmario/charlock_holmes