[REQ] Add `--enable-post-process-file` example for `nodejs-express-server`

Created by: mattnorris

Is your feature request related to a problem? Please describe.

Most generators give you an environment variable and example command in the log output for --enable-post-process-file. Generating nodejs-express-server does not.

Describe the solution you'd like

Add --enable-post-process-file example for nodejs-express-server.

Additional context

Discussed with @jimschubert and @wing328 on Slack.