Add known projects that use these bindings.

README.md

@@ -56,6 +56,12 @@ See the [hello world tutorial](https://github.com/hugopl/gtk4.cr/tree/master/tut
 For more info on how to use signals, properties, etc see the [GI-Crystal](https://github.com/hugopl/gi-crystal)
 project page, it's the binding generator used to create this binding.
 
+## Projects using these bindings
+
+- [Collision](https://github.com/GeopJr/Collision) - A GUI tool to generate, compare and verify MD5, SHA-1, SHA-256 & SHA-512 hashes.
+- [RTFM](https://github.com/hugopl/rtfm) - Gnome dash docset documentation reader.
+- [Tijolo](https://github.com/hugopl/tijolo) - Simple and fast keyboard focused IDE (version using these bindings not yet released). 
+
 ## Contributing
 
 1. Fork it (<https://github.com/hugopl/gtk4.cr/fork>)