This plugin provides completion definitions for some of the commands defined by git-extras.
The completions work by augmenting the _git completion provided by zsh. This only works with the zsh-provided _git, not the _git provided by git itself. If you have both zsh and git installed, you need to make sure that the zsh-provided _git takes precedence.
On OS X with Homebrew, you need to install git with brew install git --without-completions. Otherwise, git's _git will take precedence, and you won't see the completions for git-extras commands.