Add documentation for configuration options

[braydonf]

These configuration options can be used to change the route that the service is hosted (e.g. /api instead of /insight-api). The insight-ui options changes where the insight-api is hosted. And the caching option enables caching headers.

  "servicesConfig": {
    "insight-ui": {
      "routePrefix": "",
      "apiPrefix": "api"
    },
    "insight-api": {
      "routePrefix": "api",
      "enableCache": true
    }
  }

[braydonf]

This also relates with bitpay/bitcore-website#85

[0x2a94b5]

thx