src: supply missing comments for CLI options

A few of the CLI option values exposed as properties on the process
object were missing a comment, fix this.

PR-URL: https://github.com/nodejs/node/pull/12245


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>