docs: add

Author: yoshuawuyts

.gitignore

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+node_modules/
+coverage/
+tmp/
+npm-debug.log*
+.DS_Store

README.md

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+# sheetify-cssnext [![stability][0]][1]
+[![build status][4]][5] [![test coverage][6]][7] [![js-standard-style][10]][11]
+
+[cssnext][12] transform for [sheetify][13]. Use tomorrow's CSS syntax, today.
+
+## Installation
+```sh
+$ npm install sheetify-cssnext
+```
+
+## Usage
+```js
+const sheetify = require('sheetify')
+const path = require('path')
+
+const opts = {
+  use: [ [ 'sheetify-cssnext', { sourcemap: false } ] ],
+  basedir: __dirname
+}
+
+sheetify(path.join(__dirname, 'index.css'), opts)
+  .pipe(process.stdout)
+```
+
+## See Also
+- [cssnext][13]
+- [sheetify][13]
+
+## License
+[MIT](https://tldrlegal.com/license/mit-license)
+
+[0]: https://img.shields.io/badge/stability-experimental-orange.svg?style=flat-square
+[1]: https://nodejs.org/api/documentation.html#documentation_stability_index
+[4]: https://img.shields.io/travis/yoshuawuyts/wayfarer-www/master.svg?style=flat-square
+[5]: https://travis-ci.org/yoshuawuyts/wayfarer-www
+[6]: https://img.shields.io/codecov/c/github/yoshuawuyts/wayfarer-www/master.svg?style=flat-square
+[7]: https://codecov.io/github/yoshuawuyts/wayfarer-www
+[10]: https://img.shields.io/badge/code%20style-standard-brightgreen.svg?style=flat-square
+[11]: https://github.com/feross/standard
+[12]: https://github.com/cssnext/cssnext
+[12]: https://github.com/sheetify/sheetify