Add events.

README.md

 * [Event](https://github.com/thephpleague/event) - An event library with a focus on domain events.
 * [Hoa EventSource](https://github.com/hoaproject/Eventsource) - An event source library.
 * [Hoa WebSocket](https://github.com/hoaproject/Websocket) - Another web socket library.
+* [Pawl](https://github.com/ratchetphp/Pawl) - An asynchronous web socket client.
 * [Prooph Event Store](https://github.com/prooph/event-store) - An event source component to persist event messages
 * [PHP Defer](https://github.com/php-defer/php-defer) - Golang's defer statement for PHP.
 * [Ratchet](https://github.com/ratchetphp/Ratchet) - A web socket library.