Welcome to our new platform maintainers! (#2481)

* Add new platform maintainers to README!

* Add a codeowners file

.github/CODEOWNERS

@@ -0,0 +1,2 @@
+cibuildwheel/platforms/ios.py         @freakboy3742
+cibuildwheel/platforms/pyodide.py     @hoodmane @ryanking13 @agriyakhetarpal

README.md

@@ -312,12 +312,22 @@ Everyone interacting with the cibuildwheel project via codebase, issue tracker,
 Maintainers
 -----------
 
+Core:
+
 - Joe Rickerby [@joerick](https://github.com/joerick)
 - Yannick Jadoul [@YannickJadoul](https://github.com/YannickJadoul)
 - Matthieu Darbois [@mayeut](https://github.com/mayeut)
 - Henry Schreiner [@henryiii](https://github.com/henryiii)
 - Grzegorz Bokota [@Czaki](https://github.com/Czaki)
 
+Platform maintainers:
+
+- Russell Keith-Magee [@freakboy3742](https://github.com/freakboy3742) (iOS)
+- Agriya Khetarpal [@agriyakhetarpal](https://github.com/agriyakhetarpal) (Pyodide)
+- Hood Chatham [@hoodmane](https://github.com/hoodmane) (Pyodide)
+- Gyeongjae Choi [@ryanking13](https://github.com/ryanking13) (Pyodide)
+- Tim Felgentreff [@timfel](https://github.com/timfel) (GraalPy)
+
 Credits
 -------