Fix #7065: cli help documentation for --inspect

Adding documentation to node.1 and cli.md

PR-URL: https://github.com/nodejs/node/pull/11660


Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>