Add Pure theme

## Pure for Oh My Zsh

A super-clean and minimal theme for your Oh My Zsh-powered prompt. Based on the [Pure prompt](https://github.com/sindresorhus/pure) by [Sindre Sorhus](https://github.com/sindresorhus)

![](https://github.com/kasperisager/zsh-pure/raw/master/screenshot.png)

The repo can be found here: https://github.com/kasperisager/zsh-pure