Update README.md

Author: clue

README.md

@@ -4,6 +4,46 @@ Streaming UTF-8 parser for React PHP
 
 > Note: This project is in early alpha stage! Feel free to report any issues you encounter.
 
+## Usage
+
+### Sequencer
+
+The `Sequencer` class can be used to make sure you only get back complete, valid
+UTF-8 byte sequences when reading from a stream.
+It wraps a given `ReadableStreamInterface` and exposes its data through the same
+interface.
+
+```php
+$stdin = new Stream(STDIN, $loop);
+
+$stream = new Sequencer($stdin);
+
+$stream->on('data', function ($chunk) {
+    var_dump($chunk);
+});
+```
+
+React's streams emit chunks of data strings and make no assumption about its encoding.
+These chunks do not necessarily represent complete UTF-8 byte sequences, as a
+sequence may be broken up into multiple chunks.
+This class reassembles these sequences by buffering incomplete ones.
+
+Also, if you're merely consuming a stream and you're not in control of producing and
+ensuring valid UTF-8 data, it may as well include invalid UTF-8 byte sequences.
+This class replaces any invalid bytes in the sequence with a `?`.
+This replacement character can be given as a second paramter to the constructor:
+
+```php
+$stream = new Sequencer($stdin, 'X');
+```
+
+As such, you can be sure you never get an invalid UTF-8 byte sequence out of
+the resulting stream.
+
+Note that the stream may still contain ASCII/ANSI control characeters, as they're
+valid UTF-8.
+This binary data will be left as-is, unless you filter this at a later stage.
+
 ## Install
 
 The recommended way to install this library is [through Composer](https://getcomposer.org).