Cannot use package globally via yarn global add

[Elliot-Evans-95]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
Trying to globally install grunt. If I use yarn global add command, it will be allow me to use 'grunt' as a cli name. If I install grunt globally via npm, I can use grunt as a cli name
If the current behavior is a bug, please provide the steps to reproduce.

1. install a npm package globally (yarn global add grunt)
2. package successfully installs.
3. restarted terminal for changes.
4. type grunt in to terminal.
5. errors: zsh: command not found: grunt
   note: I have added export PATH="$PATH:$HOME/.yarn/bin" to my .zshrc file, still cannot find 'grunt'
   What is the expected behavior?
   grunt can be used on the command line.
   Please mention your node.js, yarn and operating system version.
   Mac OS X El capitain
   Installed via homebrew
   iterm2 with zsh

[wyze]

Duplicate #1321.