Correct paths, add zsh path in README.md

`README.md` listed `~/.virtualcandy/virtualcandy.sh` as the shell filed to be sourced, but I believe that's an old path as the file currently resides in `~/.virtualcandy/src/virtualcandy.sh`. Additionally I also added a mention to the `README.md` that there is a different shell file to source if you're using ZShell.