Add scmpuff to oh-my-zsh plugins

[pmastela]

Make enabling scmpuff as simple as adding scmpuff to the list of plugins in one's .zshrc. Side benefit for the project would be that it would be listed in oh-my-zsh plugins thus likely driving higher adoption.

[mroth]

scmpuff is a binary (and thus OS/platform specific), not a zsh script, so I don't believe that would work. If there is an easy way to do so, please open a PR and let me know.