Added alias for git diff.

plugins/git/git.plugin.zsh

@@ -3,6 +3,8 @@ alias g='git'
 compdef g=git
 alias gst='git status'
 compdef _git gst=git-status
+alias gd='git diff'
+compdef _git diff=git-diff
 alias gl='git pull'
 compdef _git gl=git-pull
 alias gup='git fetch && git rebase'