Update README.md

Author: clue

README.md

@@ -32,6 +32,47 @@ $loop->run();
 
 See also the [examples](examples).
 
+## Usage
+
+### Factory
+
+The `Factory` is responsible for creating your [`Resolver`](#resolver) instance.
+It also registers everything with the main [`EventLoop`](https://github.com/reactphp/event-loop#usage).
+
+```php
+$loop = React\EventLoop\Factory::create();
+$factory = new Factory($loop);
+```
+
+#### createResolver()
+
+The `createResolver()` method can be used to create a mDNS resolver instance that sends multicast DNS queries and waits for incoming unicast DNS responses. It returns a [`Resolver`](#resolver) instance.
+
+### Resolver
+
+The [`Factory`](#factory) creates instances of the `React\Dns\Resolver\Resolver` class from the [react/dns](https://github.com/reactphp/dns) package.
+
+While React's *normal* DNS resolver uses unicast UDP messages (and TCP streams) to query a given nameserver,
+this resolver instance uses multicast UDP messages to query all reachable hosts in your network.
+
+Sending queries is async (non-blocking), so you can actually send multiple DNS queries in parallel.
+The mDNS hosts will respond to each DNS query message with a DNS response message. The order is not guaranteed.
+Sending queries uses a [Promise](https://github.com/reactphp/promise)-based interface that makes it easy to react to when a query is *fulfilled*
+(i.e. either successfully resolved or rejected with an error):
+
+```php
+$resolver->lookup($hostname)->then(
+    function ($ip) {
+        // IP successfully resolved
+    },
+    function (Exception $e) {
+        // an error occured while looking up the given hostname
+    }
+});
+```
+
+Please refer to the [DNS documentation](https://github.com/reactphp/dns#readme) for more details.
+
 ## Install
 
 The recommended way to install this library is [through composer](http://getcomposer.org). [New to composer?](http://getcomposer.org/doc/00-intro.md)