doc: --enable-source-maps and prepareStackTrace are incompatible

document the fact that --enable-source-maps and prepareStackTrace are
incompatible, see #29994

PR-URL: #30046
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Author: bcoe

doc/api/cli.md

@@ -144,6 +144,9 @@ added: v12.12.0
 
 Enable experimental Source Map V3 support for stack traces.
 
+Currently, overriding `Error.prepareStackTrace` is ignored when the
+`--enable-source-maps` flag is set.
+
 ### `--es-module-specifier-resolution=mode`
 <!-- YAML
 added: v12.0.0