Docs: add per-route usage example

[Sbrjt]

Consider adding a per-route example in the doc:

var router = express.Router()

router.get('/your-route', compression(), function (req, res) {
  res.json({ message: 'This response is compressed' })
})

[bjohansebas]

I don't think we should add this example, it's more about Express topic than about how to use this package.

[lutfallah]

Consider adding a per-route example in the doc:

var router = express.Router()

router.get('/your-route', compression(), function (req, res) {
  res.json({ message: 'This response is compressed' })
})

[lutfallah]

Consider adding a per-route example in the doc:

var router = express.Router()

router.get('/your-route', compression(), function (req, res) {
  res.json({ message: 'This response is compressed' })
})