Add poise to the "Projects extending Serenity" section (#1551)

Author: vicky5124

README.md

@@ -202,6 +202,7 @@ If you use the `native_tls_backend` and you are not developing on macOS or Windo
 
 - [lavalink-rs][project:lavalink-rs]: An interface to [Lavalink][repo:lavalink], an audio sending node based on [Lavaplayer][repo:lavaplayer]
 - [Songbird][project:songbird]: An async Rust library for the Discord voice API.
+- [Poise][project:poise]: Experimental command framework, with advanced features like edit tracking, single function slash and prefix commands and flexible argument parsing.
 
 [`Cache`]: https://docs.rs/serenity/*/serenity/cache/struct.Cache.html
 [`Client::builder`]: https://docs.rs/serenity/*/serenity/client/struct.Client.html#method.builder
@@ -228,6 +229,7 @@ If you use the `native_tls_backend` and you are not developing on macOS or Windo
 [guild-badge]: https://img.shields.io/discord/381880193251409931.svg?style=flat-square&colorB=7289DA
 [project:lavalink-rs]: https://gitlab.com/vicky5124/lavalink-rs/
 [project:songbird]: https://github.com/serenity-rs/songbird
+[project:poise]: https://github.com/kangalioo/poise
 [repo:lavalink]: https://github.com/freyacodes/Lavalink
 [repo:lavaplayer]: https://github.com/sedmelluq/lavaplayer
 [logo]: https://raw.githubusercontent.com/serenity-rs/serenity/current/logo.png