Add zsh-nvm

What do you think about installing `zsh-nvm` by default?

https://github.com/lukechilds/zsh-nvm

## Guide to install

```
git clone https://github.com/lukechilds/zsh-nvm.git ~/.zsh-nvm
```

Add this to the top of `~/.zshrc.local`:

```rc
export NVM_LAZY_LOAD=true
source ~/.zsh-nvm/zsh-nvm.plugin.zsh

export NODE_ENV=development
```