cli: clarify --cpu-prof-name allowed values

Refs: https://github.com/nodejs/node/issues/57418
PR-URL: https://github.com/nodejs/node/pull/57433
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

doc/api/cli.md

@@ -501,6 +501,15 @@ $ ls *.cpuprofile
 CPU.20190409.202950.15293.0.0.cpuprofile
 ```
 
+If `--cpu-prof-name` is specified, the provided value will be used as-is; patterns such as
+`${hhmmss}` or `${pid}` are not supported.
+
+```console
+$ node --cpu-prof --cpu-prof-name 'CPU.${pid}.cpuprofile' index.js
+$ ls *.cpuprofile
+'CPU.${pid}.cpuprofile'
+```
+
 ### `--cpu-prof-dir`
 
 <!-- YAML