I'd actually show the process in reverse order; first install `underscore` through `npm`, then write a script to require and use it.

Also, the example script should be copyable/pasteable so people will actually see something printed to their console and believe it's actually working :)

```js
// npm-underscore-test.js
var _ = require('underscore');
var casper = require('casper').create();
var urls = _.uniq([
  'http://google.com/',
  'http://yahoo.com/',
  'http://google.com/'
]));

casper.start().eachThen(urls, function() {
  this.echo(this.getTitle());
});

casper.run();
```

Or something approaching/less dumb, be creative :)

Last, show the sample cli invokation, eg 

```
$ casperjs npm-underscore-test.js
Google
Yahoo!
```