Update readme.

README.md

@@ -1,15 +1,48 @@
-# util
+# util [![Build Status](https://travis-ci.org/defunctzombie/node-util.png?branch=master)](https://travis-ci.org/defunctzombie/node-util)
 
-[![Build Status](https://travis-ci.org/defunctzombie/node-util.png?branch=master)](https://travis-ci.org/defunctzombie/node-util)
+> Node.js's [util][util] module for all engines.
 
-node.js [util](http://nodejs.org/api/util.html) module as a module
+This implements the Node.js [`util`][util] module for environments that do not have it, like browsers.
 
-## install via [npm](npmjs.org)
+## Install
+
+You usually do not have to install `util` yourself. If your code runs in Node.js, `util` is built in. If your code runs in the browser, bundlers like [browserify](https://github.com/browserify/browserify) or [webpack](https://github.com/webpack/webpack) also include the `util` module.
+
+But if none of those apply, with npm do:
 
 ```shell
 npm install util
 ```
 
-## browser support
+## Usage
+
+```javascript
+var util = require('util')
+var EventEmitter = require('events')
+
+function MyClass() { EventEmitter.call(this) }
+util.inherits(MyClass, EventEmitter)
+```
+
+## Browser Support
+
+The `util` module uses ES5 features. If you need to support very old browsers like IE8, use a shim like [`es5-shim`](https://www.npmjs.com/package/es5-shim). You need both the shim and the sham versions of `es5-shim`.
+
+To use `util.promisify` and `util.callbackify`, Promises must already be available. If you need to support browsers like IE11 that do not support Promises, use a shim. [es6-promise](https://github.com/stefanpenner/es6-promise) is a popular one but there are many others available on npm.
+
+## API
+
+See the [Node.js util docs][util].  `util` currently supports the Node 8 LTS API. However, some of the methods are outdated. The `inspect` and `format` methods included in this module are a lot more simple and barebones than the ones in Node.js.
+
+## Contributing
+
+PRs are very welcome! The main way to contribute to `util` is by porting features, bugfixes and tests from Node.js. Ideally, code contributions to this module are copy-pasted from Node.js and transpiled to ES5, rather than reimplemented from scratch. Matching the Node.js code as closely as possible makes maintenance simpler when new changes land in Node.js.
+This module intends to provide exactly the same API as Node.js, so features that are not available in the core `util` module will not be accepted. Feature requests should instead be directed at [nodejs/node](https://github.com/nodejs/node) and will be added to this module once they are implemented in Node.js.
+
+If there is a difference in behaviour between Node.js's `util` module and this module, please open an issue!
+
+## License
+
+[MIT](./LICENSE)
 
-This module also works in modern browsers. If you need legacy browser support you will need to polyfill ES5 features.
+[util]: https://nodejs.org/docs/latest-v8.x/api/util.html