Github has the following recommendation for global git configuration
[alias] # Is this [-] only a comment in .gitconfig?
gb = git branch
gba = git branch -a
gc = git commit -v
gd = git diff | mate
gl = git pull
gp = git push
gst = git status
I believe what GitHub is referring to is system aliases, not '.gitconfig' aliases.
In other terms, you would need to type, like illustrated here, the following Unix command to make those 'aliases' work:
alias g=’git’ alias gb=’git branch’ alias gba=’git branch -a’ alias gc=’git commit -v’ alias gca=’git commit -v -a’ alias gd=’git diff | mate’ alias gl=’git pull’ alias gp=’git push’