Add 'www' option to start script usage (help)

I noticed there is a `www` option that can be passed into the `start` script but although it works it didn't show up in the usage text. This is just a minor enhancement so that running `./bin/start -h` shows the `www` option as follows.

```
Usage: node ./bin/start [options]

Options:
  --www, -w       Set www root directory
  --local-tld     Turn on local-tld on supported platforms
  --no-local-tld  Turn off local-tld on supported platforms
  --help, -h      Show usage information
```