Add latest post to README

Author: osa1

README.md

@@ -12,8 +12,10 @@ For introduction, see blog posts:
 
 - [Error handling in Fir][1]
 - [Throwing iterators in Fir][2]
+- [Fir is getting useful][3]
 
 [1]: https://osa1.net/posts/2025-01-18-fir-error-handling.html
 [2]: https://osa1.net/posts/2025-04-17-throwing-iterators-fir.html
+[3]: https://osa1.net/posts/2025-09-04-fir-getting-useful.html
 [tooling]: https://github.com/fir-lang/fir/issues/28
 [libs]: https://github.com/fir-lang/fir/issues/76