Update README to contain information about protocol support (#779)

README.md

@@ -14,6 +14,9 @@ Smithay aims to provide building blocks to create wayland compositors in Rust. W
 being a full-blown compositor, it'll provide objects and interfaces implementing common
 functionalities that pretty much any compositor will need, in a generic fashion.
 
+It supports the [core Wayland protocols](https://gitlab.freedesktop.org/wayland/wayland), the official [protocol extensions](https://gitlab.freedesktop.org/wayland/wayland-protocols), and *some* external extensions, such as those made by and for [wlroots](https://gitlab.freedesktop.org/wlroots/wlr-protocols) and [KDE](https://invent.kde.org/libraries/plasma-wayland-protocols)
+<!-- https://github.com/Smithay/smithay/pull/779#discussion_r993640470 https://github.com/Smithay/smithay/issues/778 -->
+
 Also:
 
 - **Documented:** Smithay strives to maintain a clear and detailed documentation of its API and its
@@ -25,6 +28,7 @@ Also:
 - **High-level:** You should be able to not have to worry about gory low-level stuff (but 
   Smithay won't stop you if you really want to dive into it).
 
+
 ## Anvil
 
 Like others, Smithay as a compositor library has its own sample compositor: anvil.
@@ -48,4 +52,4 @@ The currently available backends are:
 
 ## Contact us
 
-If you have questions or want to discuss the project with us, our main chatroom is on Matrix: [`#smithay:matrix.org`](https://matrix.to/#/#smithay:matrix.org). You can also join it via an IRC bridge, on `#smithay` on [libera.chat](https://libera.chat/).
+If you have questions or want to discuss the project with us, our main chatroom is on Matrix: [`#smithay:matrix.org`](https://matrix.to/#/#smithay:matrix.org). You can also join it via an IRC bridge, on `#smithay` on [libera.chat](https://libera.chat/).