docs(inputs.cpu): explain macos cpu support requires cgo (#11883)

plugins/inputs/cpu/README.md

@@ -2,6 +2,19 @@
 
 The `cpu` plugin gather metrics on the system CPUs.
 
+## macOS Support
+
+The [gopsutil][1] library, which is used to collect CPU data, does not support
+gathering CPU metrics without CGO on macOS. The user will see a "not
+implemented" message in this case. Builds provided by InfluxData do not build
+with CGO.
+
+Users can use the builds provided by [Homebrew][2], which build with CGO, to
+produce CPU metrics.
+
+[1]: https://github.com/shirou/gopsutil/blob/master/cpu/cpu_darwin_nocgo.go
+[2]: https://formulae.brew.sh/formula/telegraf
+
 ## Configuration
 
 ```toml @sample.conf