Update README.md

Co-authored-by: Joe Rickerby <joerick@mac.com>

README.md

@@ -38,7 +38,7 @@ What does it do?
 <sup>¹ PyPy is only supported for manylinux wheels.</sup><br>
 <sup>² Windows arm64 support is experimental.</sup><br>
 <sup>³ Alpine 3.14 and very briefly 3.15's default python3 [was not able to load](https://github.com/pypa/cibuildwheel/issues/934) musllinux wheels. This has been fixed; please upgrade the python package if using Alpine from before the fix.</sup><br>
-<sup>⁴ Cross-compilation not supported with PyPy.</sup><br>
+<sup>⁴ Cross-compilation not supported with PyPy - to build these wheels you need to run cibuildwheel on an Apple Silicon machine.</sup><br>
 
 - Builds manylinux, musllinux, macOS 10.9+, and Windows wheels for CPython and PyPy
 - Works on GitHub Actions, Azure Pipelines, Travis CI, AppVeyor, CircleCI, GitLab CI, and Cirrus CI